diff --git a/.github/workflows/test-php.yml b/.github/workflows/test-php.yml
index 7b415e9..7f60a86 100644
--- a/.github/workflows/test-php.yml
+++ b/.github/workflows/test-php.yml
@@ -59,6 +59,7 @@ jobs:
         with:
           name: ${{github.job}}-code-coverage-report-${{ matrix.composer-channel }}-${{ matrix.php-versions }}
           path: ./.coverage-html
+          include-hidden-files: true
           if-no-files-found: error
 
       - name: Upload coverage report to Codecov
diff --git a/CustomizeCommand.php b/CustomizeCommand.php
index b8c1d87..4e16a1b 100644
--- a/CustomizeCommand.php
+++ b/CustomizeCommand.php
@@ -38,7 +38,7 @@
  * Please keep this link in your project to help others find this tool.
  * Thank you!
  *
- * @see https://github.com/alexSkrypnyk/customizer
+ * @see https://github.com/AlexSkrypnyk/customizer
  *
  * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
  * @SuppressWarnings(PHPMD.TooManyPublicMethods)
@@ -71,7 +71,7 @@ class CustomizeCommand extends BaseCommand {
   public string $composerjson;
 
   /**
-   * Composer config data.
+   * Composer config data loaded before customization.
    *
    * @var array<string,mixed>
    */
@@ -113,6 +113,8 @@ protected function execute(InputInterface $input, OutputInterface $output): int
     if (empty($answers)) {
       $this->io->success($this->message('result_no_questions'));
 
+      $this->cleanupSelf();
+
       return 0;
     }
 
@@ -235,7 +237,7 @@ protected function cleanupSelf(): void {
       $should_proceed = $this->configClass::cleanup($this);
 
       if ($should_proceed === FALSE) {
-        $this->debug("Customizer's was cleanup skipped by the config class.");
+        $this->debug("Customizer's cleanup was skipped by the config class.");
 
         return;
       }
@@ -261,6 +263,13 @@ protected function cleanupSelf(): void {
     static::arrayUnsetDeep($json, ['autoload-dev', 'psr-4', 'AlexSkrypnyk\\Customizer\\Tests\\']);
     static::arrayUnsetDeep($json, ['config', 'allow-plugins', 'alexskrypnyk/customizer']);
 
+    // Remove the Customizer from the list of repositories if it was added as a
+    // local or overridden dependency.
+    // @todo Update to only remove if the package `url` path matches the current
+    // working directory.
+    static::arrayUnsetDeep($json, ['repositories']);
+    static::arrayUnsetDeep($json, ['minimum-stability']);
+
     // If the package data has changed, update the composer.json file.
     if (strcmp(serialize($this->composerjsonData), serialize($json)) !== 0) {
       $this->writeComposerJson($this->cwd . '/composer.json', $json);
@@ -309,10 +318,12 @@ protected function cleanupSelf(): void {
    *   Message.
    */
   protected function message(string $name, array $tokens = []): string {
+    // Default messages from this class.
     $messages = static::messages($this);
 
-    if (!empty($this->configClass)) {
-      if (method_exists($this->configClass, 'messages') && !is_callable([$this->configClass, 'messages'])) {
+    // Messages from the config class if 'messages' method exists.
+    if (!empty($this->configClass) && method_exists($this->configClass, 'messages')) {
+      if (!is_callable([$this->configClass, 'messages'])) {
         throw new \RuntimeException(sprintf('Optional method `messages()` exists in the config class %s but is not callable', $this->configClass));
       }
       $messages = array_replace_recursive($messages, $this->configClass::messages($this));
@@ -673,7 +684,7 @@ public static function arrayUnsetDeep(array &$array, array $path, ?string $value
    */
   public static function messages(CustomizeCommand $c): array {
     return [
-      'title' => 'Welcome to {{ package.name }} project customizer',
+      'title' => 'Welcome to the "{{ package.name }}" project customizer',
       'header' => [
         'Please answer the following questions to customize your project.',
         'You will be able to review your answers before proceeding.',
diff --git a/customize.php b/customize.php
index 1545452..5fa258c 100644
--- a/customize.php
+++ b/customize.php
@@ -59,8 +59,7 @@ public static function questions(CustomizeCommand $c): array {
         // The discover callback function is used to discover the value from the
         // environment. In this case, we use the current directory name
         // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
+        'discover' => static function (CustomizeCommand $c): string {
           $name = basename((string) getcwd());
           $org = getenv('GITHUB_ORG') ?: 'acme';
 
diff --git a/phpcs.xml b/phpcs.xml
index fa40847..a008a6b 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -31,4 +31,9 @@
         <exclude-pattern>*.TestCase\.php</exclude-pattern>
         <exclude-pattern>*.test</exclude-pattern>
     </rule>
+
+    <!-- Allow missing class description names in test fixtures. -->
+    <rule ref="Drupal.Commenting.ClassComment.Short">
+        <exclude-pattern>tests/phpunit/Fixtures</exclude-pattern>
+    </rule>
 </ruleset>
diff --git a/tests/phpunit/Dirs.php b/tests/phpunit/Dirs.php
deleted file mode 100644
index 637b1b6..0000000
--- a/tests/phpunit/Dirs.php
+++ /dev/null
@@ -1,107 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests;
-
-use AlexSkrypnyk\Customizer\Tests\Traits\FileTrait;
-use Symfony\Component\Filesystem\Filesystem;
-
-/**
- * Class to work with directories.
- */
-class Dirs {
-
-  use FileTrait;
-
-  /**
-   * Root project directory.
-   */
-  public string $root;
-
-  /**
-   * Fixtures project directory.
-   */
-  public string $fixtures;
-
-  /**
-   * Root build directory where the rest of the directories located.
-   *
-   * The "build" in this context is a place to store assets produced by a single
-   * test run.
-   */
-  public string $build;
-
-  /**
-   * Directory used as a source in the operations.
-   *
-   * Could be a copy of the current repository with custom adjustments or a
-   * fixture repository.
-   */
-  public string $repo;
-
-  /**
-   * Directory where the test will run.
-   */
-  public string $sut;
-
-  /**
-   * The file system.
-   */
-  public Filesystem $fs;
-
-  /**
-   * Dirs constructor.
-   */
-  public function __construct() {
-    $this->fs = new Filesystem();
-  }
-
-  /**
-   * Initialize locations.
-   */
-  public function initLocations(?callable $cb = NULL, string $root = NULL): void {
-    $this->root = $root ?: $this->fileFindDir('composer.json', dirname(__FILE__) . '/../..');
-
-    $this->fixtures = $this->root . '/tests/phpunit/Fixtures';
-    if (!is_dir($this->fixtures)) {
-      throw new \RuntimeException('The fixtures directory does not exist: ' . $this->fixtures);
-    }
-
-    $this->build = rtrim(sys_get_temp_dir(), DIRECTORY_SEPARATOR) . DIRECTORY_SEPARATOR . 'customizer-' . microtime(TRUE);
-    $this->sut = $this->build . '/sut';
-    $this->repo = $this->build . '/local_repo';
-
-    $this->fs->mkdir($this->build);
-    $this->fs->mkdir($this->sut);
-    $this->fs->mkdir($this->repo);
-
-    if (is_callable($cb)) {
-      // Pass the instance of Dirs to the callback instead of binding it so that
-      // the caller class could still use their own methods.
-      $cb($this);
-    }
-  }
-
-  /**
-   * Delete locations.
-   */
-  public function deleteLocations(): void {
-    $this->fs->remove($this->build);
-  }
-
-  /**
-   * Print information about locations.
-   */
-  public function printInfo(): string {
-    $lines[] = '-- LOCATIONS --';
-    $lines[] = 'Root       : ' . $this->root;
-    $lines[] = 'Fixtures   : ' . $this->fixtures;
-    $lines[] = 'Build      : ' . $this->build;
-    $lines[] = 'SUT        : ' . $this->sut;
-    $lines[] = 'Local repo : ' . $this->repo;
-
-    return implode(PHP_EOL, $lines) . PHP_EOL;
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/.ignorecontent b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/.ignorecontent
new file mode 100644
index 0000000..571e5a2
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/.ignorecontent
@@ -0,0 +1,37 @@
+# Syntax of this file is similar to .gitignore with addition of content changes
+# ignoring using ^ prefix:
+# Comments start with #.
+# file - ignore file
+# dir/ - ignore directory and all subdirectories
+# dir/* - ignore all files in directory, but not subdirectories
+# ^file - ignore content changes in file, but not the file itself
+# ^dir/ - ignore content changes in all files and subdirectories, but check that the directory itself exists
+# ^dir/* - ignore content changes in all files, but not subdirectories and check that the directory itself exists
+# !file - do not ignore file
+# !dir/ - do not ignore directory, including all subdirectories
+# !dir/* - do not ignore all files in directory, but not subdirectories
+# !^file - do not ignore content changes in file
+# !^dir/ - do not ignore content changes in all files and subdirectories
+# !^dir/* - do not ignore content changes in all files, but not subdirectories
+
+# Ignore all files by extension.
+*.log
+
+# Ignore file in root and all directories.
+f3-new-file-ignore-everywhere.txt
+
+# Ignore dir with all files, but not subdirectories.
+dir2_flat/*
+
+# Ignore all files and subdirectories in the directory.
+dir3_subdirs/*
+# But include sub-sub-directory.
+!dir3_subdirs/dir32-unignored/
+
+# Ignore directory and all subdirectories.
+dir4_full_ignore/
+
+# Ignore content in the directory.
+^dir5_content_ignore/
+# But include this file content changes for comparison.
+!^dir5_content_ignore/d5f2-unignored-content.txt
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f1.txt
new file mode 100644
index 0000000..f158938
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f1.txt
@@ -0,0 +1 @@
+d1f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f2.txt
new file mode 100644
index 0000000..0b8bacd
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir1_flat/d1f2.txt
@@ -0,0 +1 @@
+d1f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f1-ignored.txt
new file mode 100644
index 0000000..13d181a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f1-ignored.txt
@@ -0,0 +1 @@
+d3f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f2-ignored.txt
new file mode 100644
index 0000000..af655c3
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/d3f2-ignored.txt
@@ -0,0 +1,2 @@
+d3f2l1
+
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt
new file mode 100644
index 0000000..69c9854
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt
@@ -0,0 +1 @@
+d31f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt
new file mode 100644
index 0000000..bdfba81
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt
@@ -0,0 +1 @@
+d31f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt
new file mode 100644
index 0000000..4f4ce52
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt
@@ -0,0 +1 @@
+d32f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log
new file mode 100644
index 0000000..aa31929
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log
@@ -0,0 +1 @@
+d32f2l1.log only src
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt
new file mode 100644
index 0000000..3b68466
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt
@@ -0,0 +1 @@
+d32f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt
new file mode 100644
index 0000000..e8db00e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt
new file mode 100644
index 0000000..2704e6e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt
@@ -0,0 +1 @@
+d5f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt
new file mode 100644
index 0000000..e8db00e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f1.txt
new file mode 100644
index 0000000..b0bac68
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f1.txt
@@ -0,0 +1 @@
+f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f2.txt
new file mode 100644
index 0000000..47f6fa5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f2.txt
@@ -0,0 +1 @@
+f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f4-ignore-ext.log b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f4-ignore-ext.log
new file mode 100644
index 0000000..fa88711
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir1/f4-ignore-ext.log
@@ -0,0 +1 @@
+f4l1.log
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f1.txt
new file mode 100644
index 0000000..f158938
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f1.txt
@@ -0,0 +1 @@
+d1f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f2.txt
new file mode 100644
index 0000000..0b8bacd
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir1_flat/d1f2.txt
@@ -0,0 +1 @@
+d1f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f1.txt
new file mode 100644
index 0000000..a3ce084
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f1.txt
@@ -0,0 +1 @@
+d2f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f2.txt
new file mode 100644
index 0000000..ee17a17
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir2_flat/d2f2.txt
@@ -0,0 +1 @@
+d2f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f1-ignored.txt
new file mode 100644
index 0000000..13d181a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f1-ignored.txt
@@ -0,0 +1 @@
+d3f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f2-ignored.txt
new file mode 100644
index 0000000..1c4b57b
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/d3f2-ignored.txt
@@ -0,0 +1 @@
+d3f2l1-changes
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt
new file mode 100644
index 0000000..69c9854
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt
@@ -0,0 +1 @@
+d31f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt
new file mode 100644
index 0000000..bdfba81
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt
@@ -0,0 +1 @@
+d31f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt
new file mode 100644
index 0000000..4f4ce52
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt
@@ -0,0 +1 @@
+d32f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log
new file mode 100644
index 0000000..61ab7b8
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log
@@ -0,0 +1 @@
+d32f2l1.log only dst
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt
new file mode 100644
index 0000000..3b68466
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt
@@ -0,0 +1 @@
+d32f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir4_full_ignore/d4f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir4_full_ignore/d4f1.txt
new file mode 100644
index 0000000..e2139b5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir4_full_ignore/d4f1.txt
@@ -0,0 +1 @@
+d4f1l1-fully ignored
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt
new file mode 100644
index 0000000..2c5d36a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1-changed
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt
new file mode 100644
index 0000000..2704e6e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt
@@ -0,0 +1 @@
+d5f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt
new file mode 100644
index 0000000..2c5d36a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1-changed
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f1.txt
new file mode 100644
index 0000000..b0bac68
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f1.txt
@@ -0,0 +1 @@
+f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f2.txt
new file mode 100644
index 0000000..47f6fa5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f2.txt
@@ -0,0 +1 @@
+f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f4-ignore-ext.log b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f4-ignore-ext.log
new file mode 100644
index 0000000..fa88711
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f4-ignore-ext.log
@@ -0,0 +1 @@
+f4l1.log
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f5-new-file-ignore-ext.log b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f5-new-file-ignore-ext.log
new file mode 100644
index 0000000..fa88711
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_equal/dir2/f5-new-file-ignore-ext.log
@@ -0,0 +1 @@
+f4l1.log
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/.ignorecontent b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/.ignorecontent
new file mode 100644
index 0000000..571e5a2
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/.ignorecontent
@@ -0,0 +1,37 @@
+# Syntax of this file is similar to .gitignore with addition of content changes
+# ignoring using ^ prefix:
+# Comments start with #.
+# file - ignore file
+# dir/ - ignore directory and all subdirectories
+# dir/* - ignore all files in directory, but not subdirectories
+# ^file - ignore content changes in file, but not the file itself
+# ^dir/ - ignore content changes in all files and subdirectories, but check that the directory itself exists
+# ^dir/* - ignore content changes in all files, but not subdirectories and check that the directory itself exists
+# !file - do not ignore file
+# !dir/ - do not ignore directory, including all subdirectories
+# !dir/* - do not ignore all files in directory, but not subdirectories
+# !^file - do not ignore content changes in file
+# !^dir/ - do not ignore content changes in all files and subdirectories
+# !^dir/* - do not ignore content changes in all files, but not subdirectories
+
+# Ignore all files by extension.
+*.log
+
+# Ignore file in root and all directories.
+f3-new-file-ignore-everywhere.txt
+
+# Ignore dir with all files, but not subdirectories.
+dir2_flat/*
+
+# Ignore all files and subdirectories in the directory.
+dir3_subdirs/*
+# But include sub-sub-directory.
+!dir3_subdirs/dir32-unignored/
+
+# Ignore directory and all subdirectories.
+dir4_full_ignore/
+
+# Ignore content in the directory.
+^dir5_content_ignore/
+# But include this file content changes for comparison.
+!^dir5_content_ignore/d5f2-unignored-content.txt
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f1.txt
new file mode 100644
index 0000000..f158938
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f1.txt
@@ -0,0 +1 @@
+d1f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f2.txt
new file mode 100644
index 0000000..0b8bacd
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f2.txt
@@ -0,0 +1 @@
+d1f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f3-only-src.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f3-only-src.txt
new file mode 100644
index 0000000..61f88bc
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir1_flat/d1f3-only-src.txt
@@ -0,0 +1 @@
+d1f3l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f1-ignored.txt
new file mode 100644
index 0000000..13d181a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f1-ignored.txt
@@ -0,0 +1 @@
+d3f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f2-ignored.txt
new file mode 100644
index 0000000..af655c3
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/d3f2-ignored.txt
@@ -0,0 +1,2 @@
+d3f2l1
+
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt
new file mode 100644
index 0000000..69c9854
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f1-ignored.txt
@@ -0,0 +1 @@
+d31f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt
new file mode 100644
index 0000000..bdfba81
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir31/d31f2-ignored.txt
@@ -0,0 +1 @@
+d31f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt
new file mode 100644
index 0000000..4f4ce52
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f1.txt
@@ -0,0 +1 @@
+d32f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log
new file mode 100644
index 0000000..aa31929
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2-only-src.log
@@ -0,0 +1 @@
+d32f2l1.log only src
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt
new file mode 100644
index 0000000..3b68466
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir3_subdirs/dir32-unignored/d32f2.txt
@@ -0,0 +1 @@
+d32f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt
new file mode 100644
index 0000000..e8db00e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f1-ignored-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt
new file mode 100644
index 0000000..2704e6e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/d5f2-unignored-content.txt
@@ -0,0 +1 @@
+d5f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt
new file mode 100644
index 0000000..e8db00e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/dir5_content_ignore/dir51/d51f1-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f1.txt
new file mode 100644
index 0000000..b0bac68
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f1.txt
@@ -0,0 +1 @@
+f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f2.txt
new file mode 100644
index 0000000..47f6fa5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f2.txt
@@ -0,0 +1 @@
+f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f4-ignore-ext.log b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f4-ignore-ext.log
new file mode 100644
index 0000000..fa88711
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir1/f4-ignore-ext.log
@@ -0,0 +1 @@
+f4l1.log
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f1.txt
new file mode 100644
index 0000000..f158938
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f1.txt
@@ -0,0 +1 @@
+d1f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f2.txt
new file mode 100644
index 0000000..0b8bacd
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir1_flat/d1f2.txt
@@ -0,0 +1 @@
+d1f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f1.txt
new file mode 100644
index 0000000..a3ce084
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f1.txt
@@ -0,0 +1 @@
+d2f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f2.txt
new file mode 100644
index 0000000..ee17a17
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir2_flat-present-dst/d2f2.txt
@@ -0,0 +1 @@
+d2f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f1-ignored.txt
new file mode 100644
index 0000000..13d181a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f1-ignored.txt
@@ -0,0 +1 @@
+d3f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f2-ignored.txt
new file mode 100644
index 0000000..1c4b57b
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/d3f2-ignored.txt
@@ -0,0 +1 @@
+d3f2l1-changes
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt
new file mode 100644
index 0000000..69c9854
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f1-ignored.txt
@@ -0,0 +1 @@
+d31f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt
new file mode 100644
index 0000000..bdfba81
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/d31f2-ignored.txt
@@ -0,0 +1 @@
+d31f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f4-new-file-notignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f4-new-file-notignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir31/f4-new-file-notignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt
new file mode 100644
index 0000000..4f4ce52
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f1.txt
@@ -0,0 +1 @@
+d32f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log
new file mode 100644
index 0000000..61ab7b8
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2-ignore-ext-only-dst.log
@@ -0,0 +1 @@
+d32f2l1.log only dst
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt
new file mode 100644
index 0000000..affaa01
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/dir32-unignored/d32f2.txt
@@ -0,0 +1 @@
+d32f2l1-changed
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir3_subdirs/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir4_full_ignore/d4f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir4_full_ignore/d4f1.txt
new file mode 100644
index 0000000..e2139b5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir4_full_ignore/d4f1.txt
@@ -0,0 +1 @@
+d4f1l1-fully ignored
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt
new file mode 100644
index 0000000..2c5d36a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f1-ignored-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1-changed
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt
new file mode 100644
index 0000000..2704e6e
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/d5f2-unignored-content.txt
@@ -0,0 +1 @@
+d5f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt
new file mode 100644
index 0000000..2c5d36a
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f1-changed-content.txt
@@ -0,0 +1 @@
+d5f1l1-changed
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f2-new-file.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f2-new-file.txt
new file mode 100644
index 0000000..c698840
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/dir5_content_ignore/dir51/d51f2-new-file.txt
@@ -0,0 +1 @@
+d5f1l1 new file in content-ignored directory - considered as present and should fail
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f1.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f1.txt
new file mode 100644
index 0000000..b0bac68
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f1.txt
@@ -0,0 +1 @@
+f1l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f2.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f2.txt
new file mode 100644
index 0000000..47f6fa5
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f2.txt
@@ -0,0 +1 @@
+f2l1
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f3-new-file-ignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f3-new-file-ignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f3-new-file-ignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f4-new-file-notignore-everywhere.txt b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f4-new-file-notignore-everywhere.txt
new file mode 100644
index 0000000..d536218
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f4-new-file-notignore-everywhere.txt
@@ -0,0 +1 @@
+f3l1 - full ignore
diff --git a/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f5-new-file-ignore-ext.log b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f5-new-file-ignore-ext.log
new file mode 100644
index 0000000..fa88711
--- /dev/null
+++ b/tests/phpunit/Fixtures/assert_fixture_files/files_not_equal/dir2/f5-new-file-ignore-ext.log
@@ -0,0 +1 @@
+f4l1.log
diff --git a/tests/phpunit/Fixtures/command/install/base/customize.php b/tests/phpunit/Fixtures/command/install/base/customize.php
deleted file mode 100644
index e783e62..0000000
--- a/tests/phpunit/Fixtures/command/install/base/customize.php
+++ /dev/null
@@ -1,193 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-
-/**
- * Customizer configuration.
- *
- * Example configuration for the Customizer command.
- *
- * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
- *
- * @SuppressWarnings(PHPMD.UnusedFormalParameter)
- */
-class Customize {
-
-  /**
-   * A required callback with question definitions.
-   *
-   * Place questions into this method if you are using Customizer as a
-   * single-file drop-in for your scaffold project. Otherwise - place them into
-   * the configuration class.
-   *
-   * Any questions defined in the `questions()` method of the configuration
-   * class will **fully override** the questions defined here. This means that
-   * the configuration class must provide a full set of questions.
-   *
-   * See `customize.php` for an example of how to define questions.
-   *
-   * @return array<string,array<string,string|callable>>
-   *   An associative array of questions with question title as a key and the
-   *   value of array with the following keys:
-   *   - question: Required question callback function used to ask the question.
-   *     The callback receives the following arguments:
-   *     - discovered: A value discovered by the discover callback or NULL.
-   *     - answers: An associative array of all answers received so far.
-   *     - command: The CustomizeCommand object.
-   *   - discover: Optional callback function used to discover the value from
-   *     the environment. Can be an anonymous function or a method of this class
-   *     as discover<PascalCasedQuestion>. If not provided, empty string will
-   *     be passed to the question callback. The callback receives the following
-   *     arguments:
-   *     - command: The CustomizeCommand object.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
-   */
-  public static function questions(CustomizeCommand $c): array {
-    // This an example of questions that can be asked to customize the project.
-    // You can adjust this method to ask questions that are relevant to your
-    // project.
-    //
-    // In this example, we ask for the package name, description, and license.
-    //
-    // You may remove all the questions below and replace them with your own.
-    return [
-      'Name' => [
-        // The discover callback function is used to discover the value from the
-        // environment. In this case, we use the current directory name
-        // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
-          $name = basename((string) getcwd());
-          $org = getenv('GITHUB_ORG') ?: 'acme';
-
-          return $org . '/' . $name;
-        },
-        // The question callback function defines how the question is asked.
-        // In this case, we ask the user to provide a package name as a string.
-        // The discovery callback is used to provide a default value.
-        // The question callback provides a capability to validate the answer
-        // before it can be accepted by providing a validation callback.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
-          // This is a validation callback that checks if the package name is
-          // valid. If not, an \InvalidArgumentException exception is thrown
-          // with a message shown to the user.
-          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
-            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
-          }
-
-          return $value;
-        }),
-      ],
-      'Description' => [
-        // For this question, we use an answer from the previous question
-        // in the title of the question.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
-      ],
-      'License' => [
-        // For this question, we use a pre-defined list of options.
-        // For discovery, we use a separate method named 'discoverLicense'
-        // (only for the demonstration purposes; it could have been an
-        // anonymous function).
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
-          [
-            'MIT',
-            'GPL-3.0-or-later',
-            'Apache-2.0',
-          ],
-          // Note that the default value is the value discovered by the
-          // 'discoverLicense' method. If the discovery did not return a value,
-          // the default value of 'GPL-3.0-or-later' is used.
-          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
-        ),
-      ],
-    ];
-  }
-
-  /**
-   * A callback to discover the `License` value from the environment.
-   *
-   * This is an example callback, and it can be safely removed if this question
-   * is not needed.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function discoverLicense(CustomizeCommand $c): string {
-    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
-  }
-
-  /**
-   * A required callback to process all answers.
-   *
-   * This method is called after all questions have been answered and a user
-   * has confirmed the intent to proceed with the customization.
-   *
-   * Note that any manipulation of the composer.json file should be done here
-   * and then written back to the file system.
-   *
-   * @param array<string,string> $answers
-   *   Gathered answers.
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function process(array $answers, CustomizeCommand $c): void {
-    $c->debug('Updating composer configuration');
-    $json = $c->readComposerJson($c->composerjson);
-    $json['name'] = $answers['Name'];
-    $json['description'] = $answers['Description'];
-    $json['license'] = $answers['License'];
-    $c->writeComposerJson($c->composerjson, $json);
-
-    $c->debug('Removing an arbitrary file.');
-    $files = $c->finder($c->cwd)->files()->name('LICENSE');
-    foreach ($files as $file) {
-      $c->fs->remove($file->getRealPath());
-    }
-  }
-
-  /**
-   * Cleanup after the customization.
-   *
-   * By the time this method is called, all the necessary changes have been made
-   * to the project.
-   *
-   * The Customizer will remove itself from the project and will update the
-   * composer.json as required. This method allows to alter that process as
-   * needed and, if necessary, cancel the original self-cleanup.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The CustomizeCommand object.
-   *
-   * @return bool
-   *   Return FALSE to skip the further self-cleanup. Returning TRUE will
-   *   proceed with the self-cleanup.
-   */
-  public static function cleanup(CustomizeCommand $c): bool {
-    return TRUE;
-  }
-
-  /**
-   * Override some of the messages displayed to the user by Customizer.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   *
-   * @return array<string,string|array<string>>
-   *   An associative array of messages with message name as key and the message
-   *   test as a string or an array of strings.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   */
-  public static function messages(CustomizeCommand $c): array {
-    return [
-      // This is an example of a custom message that overrides the default
-      // message with name `welcome`.
-      'title' => 'Welcome to the "{{ package.name }}" project customizer',
-    ];
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/command/install_additional_cleanup/base/customize.php b/tests/phpunit/Fixtures/command/install_additional_cleanup/base/customize.php
deleted file mode 100644
index 501ad90..0000000
--- a/tests/phpunit/Fixtures/command/install_additional_cleanup/base/customize.php
+++ /dev/null
@@ -1,199 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-
-/**
- * Customizer configuration.
- *
- * Example configuration for the Customizer command.
- *
- * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
- *
- * @SuppressWarnings(PHPMD.UnusedFormalParameter)
- */
-class Customize {
-
-  /**
-   * A required callback with question definitions.
-   *
-   * Place questions into this method if you are using Customizer as a
-   * single-file drop-in for your scaffold project. Otherwise - place them into
-   * the configuration class.
-   *
-   * Any questions defined in the `questions()` method of the configuration
-   * class will **fully override** the questions defined here. This means that
-   * the configuration class must provide a full set of questions.
-   *
-   * See `customize.php` for an example of how to define questions.
-   *
-   * @return array<string,array<string,string|callable>>
-   *   An associative array of questions with question title as a key and the
-   *   value of array with the following keys:
-   *   - question: Required question callback function used to ask the question.
-   *     The callback receives the following arguments:
-   *     - discovered: A value discovered by the discover callback or NULL.
-   *     - answers: An associative array of all answers received so far.
-   *     - command: The CustomizeCommand object.
-   *   - discover: Optional callback function used to discover the value from
-   *     the environment. Can be an anonymous function or a method of this class
-   *     as discover<PascalCasedQuestion>. If not provided, empty string will
-   *     be passed to the question callback. The callback receives the following
-   *     arguments:
-   *     - command: The CustomizeCommand object.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
-   */
-  public static function questions(CustomizeCommand $c): array {
-    // This an example of questions that can be asked to customize the project.
-    // You can adjust this method to ask questions that are relevant to your
-    // project.
-    //
-    // In this example, we ask for the package name, description, and license.
-    //
-    // You may remove all the questions below and replace them with your own.
-    return [
-      'Name' => [
-        // The discover callback function is used to discover the value from the
-        // environment. In this case, we use the current directory name
-        // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
-          $name = basename((string) getcwd());
-          $org = getenv('GITHUB_ORG') ?: 'acme';
-
-          return $org . '/' . $name;
-        },
-        // The question callback function defines how the question is asked.
-        // In this case, we ask the user to provide a package name as a string.
-        // The discovery callback is used to provide a default value.
-        // The question callback provides a capability to validate the answer
-        // before it can be accepted by providing a validation callback.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
-          // This is a validation callback that checks if the package name is
-          // valid. If not, an \InvalidArgumentException exception is thrown
-          // with a message shown to the user.
-          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
-            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
-          }
-
-          return $value;
-        }),
-      ],
-      'Description' => [
-        // For this question, we use an answer from the previous question
-        // in the title of the question.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
-      ],
-      'License' => [
-        // For this question, we use a pre-defined list of options.
-        // For discovery, we use a separate method named 'discoverLicense'
-        // (only for the demonstration purposes; it could have been an
-        // anonymous function).
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
-          [
-            'MIT',
-            'GPL-3.0-or-later',
-            'Apache-2.0',
-          ],
-          // Note that the default value is the value discovered by the
-          // 'discoverLicense' method. If the discovery did not return a value,
-          // the default value of 'GPL-3.0-or-later' is used.
-          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
-        ),
-      ],
-    ];
-  }
-
-  /**
-   * A callback to discover the `License` value from the environment.
-   *
-   * This is an example callback, and it can be safely removed if this question
-   * is not needed.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function discoverLicense(CustomizeCommand $c): string {
-    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
-  }
-
-  /**
-   * A required callback to process all answers.
-   *
-   * This method is called after all questions have been answered and a user
-   * has confirmed the intent to proceed with the customization.
-   *
-   * Note that any manipulation of the composer.json file should be done here
-   * and then written back to the file system.
-   *
-   * @param array<string,string> $answers
-   *   Gathered answers.
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function process(array $answers, CustomizeCommand $c): void {
-    $c->debug('Updating composer configuration');
-    $json = $c->readComposerJson($c->composerjson);
-    $json['name'] = $answers['Name'];
-    $json['description'] = $answers['Description'];
-    $json['license'] = $answers['License'];
-    $c->writeComposerJson($c->composerjson, $json);
-
-    $c->debug('Removing an arbitrary file.');
-    $files = $c->finder($c->cwd)->files()->name('LICENSE');
-    foreach ($files as $file) {
-      $c->fs->remove($file->getRealPath());
-    }
-  }
-
-  /**
-   * Cleanup after the customization.
-   *
-   * By the time this method is called, all the necessary changes have been made
-   * to the project.
-   *
-   * The Customizer will remove itself from the project and will update the
-   * composer.json as required. This method allows to alter that process as
-   * needed and, if necessary, cancel the original self-cleanup.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The CustomizeCommand object.
-   *
-   * @return bool
-   *   Return FALSE to skip the further self-cleanup. Returning TRUE will
-   *   proceed with the self-cleanup.
-   */
-  public static function cleanup(CustomizeCommand $c): bool {
-    if ($c->isComposerDependenciesInstalled) {
-      $json = $c->readComposerJson($c->composerjson);
-      $json['minimum-stability'] = 'beta';
-      $c->writeComposerJson($c->composerjson, $json);
-    }
-
-    return TRUE;
-  }
-
-  /**
-   * Override some of the messages displayed to the user by Customizer.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   *
-   * @return array<string,string|array<string>>
-   *   An associative array of messages with message name as key and the message
-   *   test as a string or an array of strings.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   */
-  public static function messages(CustomizeCommand $c): array {
-    return [
-      // This is an example of a custom message that overrides the default
-      // message with name `welcome`.
-      'title' => 'Welcome to the "{{ package.name }}" project customizer',
-    ];
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/command/install_additional_cleanup/expected/composer.json b/tests/phpunit/Fixtures/command/install_additional_cleanup/expected/composer.json
deleted file mode 100644
index 7e09f03..0000000
--- a/tests/phpunit/Fixtures/command/install_additional_cleanup/expected/composer.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-    "name": "testorg/testpackage",
-    "description": "Test description",
-    "type": "project",
-    "license": "MIT",
-    "require": {
-        "php": ">=8.2",
-        "monolog/monolog": "^2.0"
-    },
-    "minimum-stability": "beta"
-}
diff --git a/tests/phpunit/Fixtures/command/install_sub_dir/base/composer.json b/tests/phpunit/Fixtures/command/install_sub_dir/base/composer.json
deleted file mode 100644
index 685dd21..0000000
--- a/tests/phpunit/Fixtures/command/install_sub_dir/base/composer.json
+++ /dev/null
@@ -1,19 +0,0 @@
-{
-    "name": "yourorg/yourtempaltepackage",
-    "description": "Your template package description",
-    "type": "project",
-    "license": "proprietary",
-    "require": {
-        "php": ">=8.2",
-        "monolog/monolog": "^2.0"
-    },
-    "require-dev": {
-        "alexskrypnyk/customizer": "^0.2"
-    },
-    "minimum-stability": "dev",
-    "config": {
-        "allow-plugins": {
-            "alexskrypnyk/customizer": true
-        }
-    }
-}
diff --git a/tests/phpunit/Fixtures/command/install_sub_dir/base/customize.php b/tests/phpunit/Fixtures/command/install_sub_dir/base/customize.php
deleted file mode 100644
index e783e62..0000000
--- a/tests/phpunit/Fixtures/command/install_sub_dir/base/customize.php
+++ /dev/null
@@ -1,193 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-
-/**
- * Customizer configuration.
- *
- * Example configuration for the Customizer command.
- *
- * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
- *
- * @SuppressWarnings(PHPMD.UnusedFormalParameter)
- */
-class Customize {
-
-  /**
-   * A required callback with question definitions.
-   *
-   * Place questions into this method if you are using Customizer as a
-   * single-file drop-in for your scaffold project. Otherwise - place them into
-   * the configuration class.
-   *
-   * Any questions defined in the `questions()` method of the configuration
-   * class will **fully override** the questions defined here. This means that
-   * the configuration class must provide a full set of questions.
-   *
-   * See `customize.php` for an example of how to define questions.
-   *
-   * @return array<string,array<string,string|callable>>
-   *   An associative array of questions with question title as a key and the
-   *   value of array with the following keys:
-   *   - question: Required question callback function used to ask the question.
-   *     The callback receives the following arguments:
-   *     - discovered: A value discovered by the discover callback or NULL.
-   *     - answers: An associative array of all answers received so far.
-   *     - command: The CustomizeCommand object.
-   *   - discover: Optional callback function used to discover the value from
-   *     the environment. Can be an anonymous function or a method of this class
-   *     as discover<PascalCasedQuestion>. If not provided, empty string will
-   *     be passed to the question callback. The callback receives the following
-   *     arguments:
-   *     - command: The CustomizeCommand object.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
-   */
-  public static function questions(CustomizeCommand $c): array {
-    // This an example of questions that can be asked to customize the project.
-    // You can adjust this method to ask questions that are relevant to your
-    // project.
-    //
-    // In this example, we ask for the package name, description, and license.
-    //
-    // You may remove all the questions below and replace them with your own.
-    return [
-      'Name' => [
-        // The discover callback function is used to discover the value from the
-        // environment. In this case, we use the current directory name
-        // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
-          $name = basename((string) getcwd());
-          $org = getenv('GITHUB_ORG') ?: 'acme';
-
-          return $org . '/' . $name;
-        },
-        // The question callback function defines how the question is asked.
-        // In this case, we ask the user to provide a package name as a string.
-        // The discovery callback is used to provide a default value.
-        // The question callback provides a capability to validate the answer
-        // before it can be accepted by providing a validation callback.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
-          // This is a validation callback that checks if the package name is
-          // valid. If not, an \InvalidArgumentException exception is thrown
-          // with a message shown to the user.
-          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
-            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
-          }
-
-          return $value;
-        }),
-      ],
-      'Description' => [
-        // For this question, we use an answer from the previous question
-        // in the title of the question.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
-      ],
-      'License' => [
-        // For this question, we use a pre-defined list of options.
-        // For discovery, we use a separate method named 'discoverLicense'
-        // (only for the demonstration purposes; it could have been an
-        // anonymous function).
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
-          [
-            'MIT',
-            'GPL-3.0-or-later',
-            'Apache-2.0',
-          ],
-          // Note that the default value is the value discovered by the
-          // 'discoverLicense' method. If the discovery did not return a value,
-          // the default value of 'GPL-3.0-or-later' is used.
-          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
-        ),
-      ],
-    ];
-  }
-
-  /**
-   * A callback to discover the `License` value from the environment.
-   *
-   * This is an example callback, and it can be safely removed if this question
-   * is not needed.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function discoverLicense(CustomizeCommand $c): string {
-    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
-  }
-
-  /**
-   * A required callback to process all answers.
-   *
-   * This method is called after all questions have been answered and a user
-   * has confirmed the intent to proceed with the customization.
-   *
-   * Note that any manipulation of the composer.json file should be done here
-   * and then written back to the file system.
-   *
-   * @param array<string,string> $answers
-   *   Gathered answers.
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function process(array $answers, CustomizeCommand $c): void {
-    $c->debug('Updating composer configuration');
-    $json = $c->readComposerJson($c->composerjson);
-    $json['name'] = $answers['Name'];
-    $json['description'] = $answers['Description'];
-    $json['license'] = $answers['License'];
-    $c->writeComposerJson($c->composerjson, $json);
-
-    $c->debug('Removing an arbitrary file.');
-    $files = $c->finder($c->cwd)->files()->name('LICENSE');
-    foreach ($files as $file) {
-      $c->fs->remove($file->getRealPath());
-    }
-  }
-
-  /**
-   * Cleanup after the customization.
-   *
-   * By the time this method is called, all the necessary changes have been made
-   * to the project.
-   *
-   * The Customizer will remove itself from the project and will update the
-   * composer.json as required. This method allows to alter that process as
-   * needed and, if necessary, cancel the original self-cleanup.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The CustomizeCommand object.
-   *
-   * @return bool
-   *   Return FALSE to skip the further self-cleanup. Returning TRUE will
-   *   proceed with the self-cleanup.
-   */
-  public static function cleanup(CustomizeCommand $c): bool {
-    return TRUE;
-  }
-
-  /**
-   * Override some of the messages displayed to the user by Customizer.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   *
-   * @return array<string,string|array<string>>
-   *   An associative array of messages with message name as key and the message
-   *   test as a string or an array of strings.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   */
-  public static function messages(CustomizeCommand $c): array {
-    return [
-      // This is an example of a custom message that overrides the default
-      // message with name `welcome`.
-      'title' => 'Welcome to the "{{ package.name }}" project customizer',
-    ];
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/command/no_install/base/customize.php b/tests/phpunit/Fixtures/command/no_install/base/customize.php
deleted file mode 100644
index 1545452..0000000
--- a/tests/phpunit/Fixtures/command/no_install/base/customize.php
+++ /dev/null
@@ -1,201 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-
-/**
- * Customizer configuration.
- *
- * Example configuration for the Customizer command.
- *
- * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
- *
- * @SuppressWarnings(PHPMD.UnusedFormalParameter)
- */
-class Customize {
-
-  /**
-   * A required callback with question definitions.
-   *
-   * Place questions into this method if you are using Customizer as a
-   * single-file drop-in for your scaffold project. Otherwise - place them into
-   * the configuration class.
-   *
-   * Any questions defined in the `questions()` method of the configuration
-   * class will **fully override** the questions defined here. This means that
-   * the configuration class must provide a full set of questions.
-   *
-   * See `customize.php` for an example of how to define questions.
-   *
-   * @return array<string,array<string,string|callable>>
-   *   An associative array of questions with question title as a key and the
-   *   value of array with the following keys:
-   *   - question: Required question callback function used to ask the question.
-   *     The callback receives the following arguments:
-   *     - discovered: A value discovered by the discover callback or NULL.
-   *     - answers: An associative array of all answers received so far.
-   *     - command: The CustomizeCommand object.
-   *   - discover: Optional callback function used to discover the value from
-   *     the environment. Can be an anonymous function or a method of this class
-   *     as discover<PascalCasedQuestion>. If not provided, empty string will
-   *     be passed to the question callback. The callback receives the following
-   *     arguments:
-   *     - command: The CustomizeCommand object.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
-   */
-  public static function questions(CustomizeCommand $c): array {
-    // This an example of questions that can be asked to customize the project.
-    // You can adjust this method to ask questions that are relevant to your
-    // project.
-    //
-    // In this example, we ask for the package name, description, and license.
-    //
-    // You may remove all the questions below and replace them with your own.
-    return [
-      'Name' => [
-        // The discover callback function is used to discover the value from the
-        // environment. In this case, we use the current directory name
-        // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
-          $name = basename((string) getcwd());
-          $org = getenv('GITHUB_ORG') ?: 'acme';
-
-          return $org . '/' . $name;
-        },
-        // The question callback function defines how the question is asked.
-        // In this case, we ask the user to provide a package name as a string.
-        // The discovery callback is used to provide a default value.
-        // The question callback provides a capability to validate the answer
-        // before it can be accepted by providing a validation callback.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
-          // This is a validation callback that checks if the package name is
-          // valid. If not, an \InvalidArgumentException exception is thrown
-          // with a message shown to the user.
-          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
-            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
-          }
-
-          return $value;
-        }),
-      ],
-      'Description' => [
-        // For this question, we use an answer from the previous question
-        // in the title of the question.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
-      ],
-      'License' => [
-        // For this question, we use a pre-defined list of options.
-        // For discovery, we use a separate method named 'discoverLicense'
-        // (only for the demonstration purposes; it could have been an
-        // anonymous function).
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
-          [
-            'MIT',
-            'GPL-3.0-or-later',
-            'Apache-2.0',
-          ],
-          // Note that the default value is the value discovered by the
-          // 'discoverLicense' method. If the discovery did not return a value,
-          // the default value of 'GPL-3.0-or-later' is used.
-          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
-        ),
-      ],
-    ];
-  }
-
-  /**
-   * A callback to discover the `License` value from the environment.
-   *
-   * This is an example callback, and it can be safely removed if this question
-   * is not needed.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function discoverLicense(CustomizeCommand $c): string {
-    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
-  }
-
-  /**
-   * A required callback to process all answers.
-   *
-   * This method is called after all questions have been answered and a user
-   * has confirmed the intent to proceed with the customization.
-   *
-   * Note that any manipulation of the composer.json file should be done here
-   * and then written back to the file system.
-   *
-   * @param array<string,string> $answers
-   *   Gathered answers.
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function process(array $answers, CustomizeCommand $c): void {
-    $c->debug('Updating composer configuration');
-    $json = $c->readComposerJson($c->composerjson);
-    $json['name'] = $answers['Name'];
-    $json['description'] = $answers['Description'];
-    $json['license'] = $answers['License'];
-    $c->writeComposerJson($c->composerjson, $json);
-
-    $c->debug('Removing an arbitrary file.');
-    $files = $c->finder($c->cwd)->files()->name('LICENSE');
-    foreach ($files as $file) {
-      $c->fs->remove($file->getRealPath());
-    }
-  }
-
-  /**
-   * Cleanup after the customization.
-   *
-   * By the time this method is called, all the necessary changes have been made
-   * to the project.
-   *
-   * The Customizer will remove itself from the project and will update the
-   * composer.json as required. This method allows to alter that process as
-   * needed and, if necessary, cancel the original self-cleanup.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The CustomizeCommand object.
-   *
-   * @return bool
-   *   Return FALSE to skip the further self-cleanup. Returning TRUE will
-   *   proceed with the self-cleanup.
-   */
-  public static function cleanup(CustomizeCommand $c): bool {
-    if ($c->isComposerDependenciesInstalled) {
-      $c->debug('Add an example flag to composer.json.');
-      $json = $c->readComposerJson($c->composerjson);
-      $json['extra'] = is_array($json['extra']) ? $json['extra'] : [];
-      $json['extra']['customizer'] = TRUE;
-      $c->writeComposerJson($c->composerjson, $json);
-    }
-
-    return TRUE;
-  }
-
-  /**
-   * Override some of the messages displayed to the user by Customizer.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   *
-   * @return array<string,string|array<string>>
-   *   An associative array of messages with message name as key and the message
-   *   test as a string or an array of strings.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   */
-  public static function messages(CustomizeCommand $c): array {
-    return [
-      // This is an example of a custom message that overrides the default
-      // message with name `welcome`.
-      'title' => 'Welcome to the "{{ package.name }}" project customizer',
-    ];
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/command/no_install_sub_dir/base/customize.php b/tests/phpunit/Fixtures/command/no_install_sub_dir/base/customize.php
deleted file mode 100644
index 1545452..0000000
--- a/tests/phpunit/Fixtures/command/no_install_sub_dir/base/customize.php
+++ /dev/null
@@ -1,201 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-
-/**
- * Customizer configuration.
- *
- * Example configuration for the Customizer command.
- *
- * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
- *
- * @SuppressWarnings(PHPMD.UnusedFormalParameter)
- */
-class Customize {
-
-  /**
-   * A required callback with question definitions.
-   *
-   * Place questions into this method if you are using Customizer as a
-   * single-file drop-in for your scaffold project. Otherwise - place them into
-   * the configuration class.
-   *
-   * Any questions defined in the `questions()` method of the configuration
-   * class will **fully override** the questions defined here. This means that
-   * the configuration class must provide a full set of questions.
-   *
-   * See `customize.php` for an example of how to define questions.
-   *
-   * @return array<string,array<string,string|callable>>
-   *   An associative array of questions with question title as a key and the
-   *   value of array with the following keys:
-   *   - question: Required question callback function used to ask the question.
-   *     The callback receives the following arguments:
-   *     - discovered: A value discovered by the discover callback or NULL.
-   *     - answers: An associative array of all answers received so far.
-   *     - command: The CustomizeCommand object.
-   *   - discover: Optional callback function used to discover the value from
-   *     the environment. Can be an anonymous function or a method of this class
-   *     as discover<PascalCasedQuestion>. If not provided, empty string will
-   *     be passed to the question callback. The callback receives the following
-   *     arguments:
-   *     - command: The CustomizeCommand object.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
-   */
-  public static function questions(CustomizeCommand $c): array {
-    // This an example of questions that can be asked to customize the project.
-    // You can adjust this method to ask questions that are relevant to your
-    // project.
-    //
-    // In this example, we ask for the package name, description, and license.
-    //
-    // You may remove all the questions below and replace them with your own.
-    return [
-      'Name' => [
-        // The discover callback function is used to discover the value from the
-        // environment. In this case, we use the current directory name
-        // and the GITHUB_ORG environment variable to generate the package name.
-        // @phpstan-ignore-next-line
-        'discover' => static function (CustomizeCommand $c): ?string {
-          $name = basename((string) getcwd());
-          $org = getenv('GITHUB_ORG') ?: 'acme';
-
-          return $org . '/' . $name;
-        },
-        // The question callback function defines how the question is asked.
-        // In this case, we ask the user to provide a package name as a string.
-        // The discovery callback is used to provide a default value.
-        // The question callback provides a capability to validate the answer
-        // before it can be accepted by providing a validation callback.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
-          // This is a validation callback that checks if the package name is
-          // valid. If not, an \InvalidArgumentException exception is thrown
-          // with a message shown to the user.
-          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
-            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
-          }
-
-          return $value;
-        }),
-      ],
-      'Description' => [
-        // For this question, we use an answer from the previous question
-        // in the title of the question.
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
-      ],
-      'License' => [
-        // For this question, we use a pre-defined list of options.
-        // For discovery, we use a separate method named 'discoverLicense'
-        // (only for the demonstration purposes; it could have been an
-        // anonymous function).
-        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
-          [
-            'MIT',
-            'GPL-3.0-or-later',
-            'Apache-2.0',
-          ],
-          // Note that the default value is the value discovered by the
-          // 'discoverLicense' method. If the discovery did not return a value,
-          // the default value of 'GPL-3.0-or-later' is used.
-          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
-        ),
-      ],
-    ];
-  }
-
-  /**
-   * A callback to discover the `License` value from the environment.
-   *
-   * This is an example callback, and it can be safely removed if this question
-   * is not needed.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function discoverLicense(CustomizeCommand $c): string {
-    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
-  }
-
-  /**
-   * A required callback to process all answers.
-   *
-   * This method is called after all questions have been answered and a user
-   * has confirmed the intent to proceed with the customization.
-   *
-   * Note that any manipulation of the composer.json file should be done here
-   * and then written back to the file system.
-   *
-   * @param array<string,string> $answers
-   *   Gathered answers.
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   */
-  public static function process(array $answers, CustomizeCommand $c): void {
-    $c->debug('Updating composer configuration');
-    $json = $c->readComposerJson($c->composerjson);
-    $json['name'] = $answers['Name'];
-    $json['description'] = $answers['Description'];
-    $json['license'] = $answers['License'];
-    $c->writeComposerJson($c->composerjson, $json);
-
-    $c->debug('Removing an arbitrary file.');
-    $files = $c->finder($c->cwd)->files()->name('LICENSE');
-    foreach ($files as $file) {
-      $c->fs->remove($file->getRealPath());
-    }
-  }
-
-  /**
-   * Cleanup after the customization.
-   *
-   * By the time this method is called, all the necessary changes have been made
-   * to the project.
-   *
-   * The Customizer will remove itself from the project and will update the
-   * composer.json as required. This method allows to alter that process as
-   * needed and, if necessary, cancel the original self-cleanup.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The CustomizeCommand object.
-   *
-   * @return bool
-   *   Return FALSE to skip the further self-cleanup. Returning TRUE will
-   *   proceed with the self-cleanup.
-   */
-  public static function cleanup(CustomizeCommand $c): bool {
-    if ($c->isComposerDependenciesInstalled) {
-      $c->debug('Add an example flag to composer.json.');
-      $json = $c->readComposerJson($c->composerjson);
-      $json['extra'] = is_array($json['extra']) ? $json['extra'] : [];
-      $json['extra']['customizer'] = TRUE;
-      $c->writeComposerJson($c->composerjson, $json);
-    }
-
-    return TRUE;
-  }
-
-  /**
-   * Override some of the messages displayed to the user by Customizer.
-   *
-   * @param \AlexSkrypnyk\Customizer\CustomizeCommand $c
-   *   The Customizer instance.
-   *
-   * @return array<string,string|array<string>>
-   *   An associative array of messages with message name as key and the message
-   *   test as a string or an array of strings.
-   *
-   * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-   */
-  public static function messages(CustomizeCommand $c): array {
-    return [
-      // This is an example of a custom message that overrides the default
-      // message with name `welcome`.
-      'title' => 'Welcome to the "{{ package.name }}" project customizer',
-    ];
-  }
-
-}
diff --git a/tests/phpunit/Fixtures/command/install_additional_cleanup/base/composer.json b/tests/phpunit/Fixtures/install/base/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/install_additional_cleanup/base/composer.json
rename to tests/phpunit/Fixtures/install/base/composer.json
index 685dd21..8720161 100644
--- a/tests/phpunit/Fixtures/command/install_additional_cleanup/base/composer.json
+++ b/tests/phpunit/Fixtures/install/base/composer.json
@@ -8,9 +8,8 @@
         "monolog/monolog": "^2.0"
     },
     "require-dev": {
-        "alexskrypnyk/customizer": "^0.2"
+        "alexskrypnyk/customizer": "*"
     },
-    "minimum-stability": "dev",
     "config": {
         "allow-plugins": {
             "alexskrypnyk/customizer": true
diff --git a/tests/phpunit/Fixtures/install/base/customize.php b/tests/phpunit/Fixtures/install/base/customize.php
new file mode 100644
index 0000000..22c1e69
--- /dev/null
+++ b/tests/phpunit/Fixtures/install/base/customize.php
@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+use AlexSkrypnyk\Customizer\CustomizeCommand;
+
+/**
+ * Customizer configuration.
+ *
+ * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
+ *
+ * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+ */
+class Customize {
+
+  public static function questions(CustomizeCommand $c): array {
+    return [
+      'Name' => [
+        'discover' => static function (CustomizeCommand $c): string {
+          $name = basename((string) getcwd());
+          $org = getenv('GITHUB_ORG') ?: 'acme';
+
+          return $org . '/' . $name;
+        },
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
+          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
+            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
+          }
+
+          return $value;
+        }),
+      ],
+      'Description' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
+      ],
+      'License' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
+          [
+            'MIT',
+            'GPL-3.0-or-later',
+            'Apache-2.0',
+          ],
+          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
+        ),
+      ],
+    ];
+  }
+
+  public static function discoverLicense(CustomizeCommand $c): string {
+    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
+  }
+
+  public static function process(array $answers, CustomizeCommand $c): void {
+    $c->debug('Updating composer configuration');
+    $json = $c->readComposerJson($c->composerjson);
+    $json['name'] = $answers['Name'];
+    $json['description'] = $answers['Description'];
+    $json['license'] = $answers['License'];
+    $c->writeComposerJson($c->composerjson, $json);
+
+    $c->debug('Removing an arbitrary file.');
+    $files = $c->finder($c->cwd)->files()->name('LICENSE');
+    foreach ($files as $file) {
+      $c->fs->remove($file->getRealPath());
+    }
+  }
+
+  public static function cleanup(CustomizeCommand $c): bool {
+    return TRUE;
+  }
+
+  public static function messages(CustomizeCommand $c): array {
+    return [
+      'title' => 'Greetings from the customizer for the "{{ package.name }}" project',
+    ];
+  }
+
+}
diff --git a/tests/phpunit/Fixtures/install/expected/.ignorecontent b/tests/phpunit/Fixtures/install/expected/.ignorecontent
new file mode 100644
index 0000000..98610ec
--- /dev/null
+++ b/tests/phpunit/Fixtures/install/expected/.ignorecontent
@@ -0,0 +1,2 @@
+vendor/
+^composer.lock
diff --git a/tests/phpunit/Fixtures/command/no_install/expected/composer.json b/tests/phpunit/Fixtures/install/expected/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/no_install/expected/composer.json
rename to tests/phpunit/Fixtures/install/expected/composer.json
index 6540581..c9da9a7 100644
--- a/tests/phpunit/Fixtures/command/no_install/expected/composer.json
+++ b/tests/phpunit/Fixtures/install/expected/composer.json
@@ -6,6 +6,5 @@
     "require": {
         "php": ">=8.2",
         "monolog/monolog": "^2.0"
-    },
-    "minimum-stability": "dev"
+    }
 }
diff --git a/tests/phpunit/Fixtures/install/expected/composer.lock b/tests/phpunit/Fixtures/install/expected/composer.lock
new file mode 100644
index 0000000..d349f0c
--- /dev/null
+++ b/tests/phpunit/Fixtures/install/expected/composer.lock
@@ -0,0 +1 @@
+IGNORECONTENT
diff --git a/tests/phpunit/Fixtures/command/install/base/composer.json b/tests/phpunit/Fixtures/install_additional_cleanup/base/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/install/base/composer.json
rename to tests/phpunit/Fixtures/install_additional_cleanup/base/composer.json
index 685dd21..8720161 100644
--- a/tests/phpunit/Fixtures/command/install/base/composer.json
+++ b/tests/phpunit/Fixtures/install_additional_cleanup/base/composer.json
@@ -8,9 +8,8 @@
         "monolog/monolog": "^2.0"
     },
     "require-dev": {
-        "alexskrypnyk/customizer": "^0.2"
+        "alexskrypnyk/customizer": "*"
     },
-    "minimum-stability": "dev",
     "config": {
         "allow-plugins": {
             "alexskrypnyk/customizer": true
diff --git a/tests/phpunit/Fixtures/install_additional_cleanup/base/customize.php b/tests/phpunit/Fixtures/install_additional_cleanup/base/customize.php
new file mode 100644
index 0000000..f6501a1
--- /dev/null
+++ b/tests/phpunit/Fixtures/install_additional_cleanup/base/customize.php
@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+use AlexSkrypnyk\Customizer\CustomizeCommand;
+
+/**
+ * Customizer configuration.
+ *
+ * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
+ *
+ * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+ */
+class Customize {
+
+  public static function questions(CustomizeCommand $c): array {
+    return [
+      'Name' => [
+        'discover' => static function (CustomizeCommand $c): string {
+          $name = basename((string) getcwd());
+          $org = getenv('GITHUB_ORG') ?: 'acme';
+
+          return $org . '/' . $name;
+        },
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
+          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
+            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
+          }
+
+          return $value;
+        }),
+      ],
+      'Description' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
+      ],
+      'License' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
+          [
+            'MIT',
+            'GPL-3.0-or-later',
+            'Apache-2.0',
+          ],
+          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
+        ),
+      ],
+    ];
+  }
+
+  public static function discoverLicense(CustomizeCommand $c): string {
+    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
+  }
+
+  public static function process(array $answers, CustomizeCommand $c): void {
+    $c->debug('Updating composer configuration');
+    $json = $c->readComposerJson($c->composerjson);
+    $json['name'] = $answers['Name'];
+    $json['description'] = $answers['Description'];
+    $json['license'] = $answers['License'];
+    $c->writeComposerJson($c->composerjson, $json);
+
+    $c->debug('Removing an arbitrary file.');
+    $files = $c->finder($c->cwd)->files()->name('LICENSE');
+    foreach ($files as $file) {
+      $c->fs->remove($file->getRealPath());
+    }
+  }
+
+  public static function cleanup(CustomizeCommand $c): bool {
+    if ($c->isComposerDependenciesInstalled) {
+      $json = $c->readComposerJson($c->composerjson);
+      $json['homepage'] = 'https://example.com';
+      $c->writeComposerJson($c->composerjson, $json);
+    }
+
+    return TRUE;
+  }
+
+}
diff --git a/tests/phpunit/Fixtures/install_additional_cleanup/expected/.ignorecontent b/tests/phpunit/Fixtures/install_additional_cleanup/expected/.ignorecontent
new file mode 100644
index 0000000..98610ec
--- /dev/null
+++ b/tests/phpunit/Fixtures/install_additional_cleanup/expected/.ignorecontent
@@ -0,0 +1,2 @@
+vendor/
+^composer.lock
diff --git a/tests/phpunit/Fixtures/command/install_sub_dir/expected/composer.json b/tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.json
similarity index 84%
rename from tests/phpunit/Fixtures/command/install_sub_dir/expected/composer.json
rename to tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.json
index 6540581..9b83e9f 100644
--- a/tests/phpunit/Fixtures/command/install_sub_dir/expected/composer.json
+++ b/tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.json
@@ -7,5 +7,5 @@
         "php": ">=8.2",
         "monolog/monolog": "^2.0"
     },
-    "minimum-stability": "dev"
+    "homepage": "https://example.com"
 }
diff --git a/tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.lock b/tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.lock
new file mode 100644
index 0000000..d349f0c
--- /dev/null
+++ b/tests/phpunit/Fixtures/install_additional_cleanup/expected/composer.lock
@@ -0,0 +1 @@
+IGNORECONTENT
diff --git a/tests/phpunit/Fixtures/command/install_no_config_file/base/composer.json b/tests/phpunit/Fixtures/install_no_config_file/base/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/install_no_config_file/base/composer.json
rename to tests/phpunit/Fixtures/install_no_config_file/base/composer.json
index 685dd21..8720161 100644
--- a/tests/phpunit/Fixtures/command/install_no_config_file/base/composer.json
+++ b/tests/phpunit/Fixtures/install_no_config_file/base/composer.json
@@ -8,9 +8,8 @@
         "monolog/monolog": "^2.0"
     },
     "require-dev": {
-        "alexskrypnyk/customizer": "^0.2"
+        "alexskrypnyk/customizer": "*"
     },
-    "minimum-stability": "dev",
     "config": {
         "allow-plugins": {
             "alexskrypnyk/customizer": true
diff --git a/tests/phpunit/Fixtures/install_no_config_file/expected/.ignorecontent b/tests/phpunit/Fixtures/install_no_config_file/expected/.ignorecontent
new file mode 100644
index 0000000..98610ec
--- /dev/null
+++ b/tests/phpunit/Fixtures/install_no_config_file/expected/.ignorecontent
@@ -0,0 +1,2 @@
+vendor/
+^composer.lock
diff --git a/tests/phpunit/Fixtures/command/install_no_config_file/expected/composer.json b/tests/phpunit/Fixtures/install_no_config_file/expected/composer.json
similarity index 53%
rename from tests/phpunit/Fixtures/command/install_no_config_file/expected/composer.json
rename to tests/phpunit/Fixtures/install_no_config_file/expected/composer.json
index 685dd21..a0a9763 100644
--- a/tests/phpunit/Fixtures/command/install_no_config_file/expected/composer.json
+++ b/tests/phpunit/Fixtures/install_no_config_file/expected/composer.json
@@ -6,14 +6,5 @@
     "require": {
         "php": ">=8.2",
         "monolog/monolog": "^2.0"
-    },
-    "require-dev": {
-        "alexskrypnyk/customizer": "^0.2"
-    },
-    "minimum-stability": "dev",
-    "config": {
-        "allow-plugins": {
-            "alexskrypnyk/customizer": true
-        }
     }
 }
diff --git a/tests/phpunit/Fixtures/install_no_config_file/expected/composer.lock b/tests/phpunit/Fixtures/install_no_config_file/expected/composer.lock
new file mode 100644
index 0000000..d349f0c
--- /dev/null
+++ b/tests/phpunit/Fixtures/install_no_config_file/expected/composer.lock
@@ -0,0 +1 @@
+IGNORECONTENT
diff --git a/tests/phpunit/Fixtures/command/no_install/base/composer.json b/tests/phpunit/Fixtures/no_install/base/composer.json
similarity index 100%
rename from tests/phpunit/Fixtures/command/no_install/base/composer.json
rename to tests/phpunit/Fixtures/no_install/base/composer.json
diff --git a/tests/phpunit/Fixtures/no_install/base/customize.php b/tests/phpunit/Fixtures/no_install/base/customize.php
new file mode 100644
index 0000000..22c1e69
--- /dev/null
+++ b/tests/phpunit/Fixtures/no_install/base/customize.php
@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+use AlexSkrypnyk\Customizer\CustomizeCommand;
+
+/**
+ * Customizer configuration.
+ *
+ * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
+ *
+ * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+ */
+class Customize {
+
+  public static function questions(CustomizeCommand $c): array {
+    return [
+      'Name' => [
+        'discover' => static function (CustomizeCommand $c): string {
+          $name = basename((string) getcwd());
+          $org = getenv('GITHUB_ORG') ?: 'acme';
+
+          return $org . '/' . $name;
+        },
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
+          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
+            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
+          }
+
+          return $value;
+        }),
+      ],
+      'Description' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
+      ],
+      'License' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
+          [
+            'MIT',
+            'GPL-3.0-or-later',
+            'Apache-2.0',
+          ],
+          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
+        ),
+      ],
+    ];
+  }
+
+  public static function discoverLicense(CustomizeCommand $c): string {
+    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
+  }
+
+  public static function process(array $answers, CustomizeCommand $c): void {
+    $c->debug('Updating composer configuration');
+    $json = $c->readComposerJson($c->composerjson);
+    $json['name'] = $answers['Name'];
+    $json['description'] = $answers['Description'];
+    $json['license'] = $answers['License'];
+    $c->writeComposerJson($c->composerjson, $json);
+
+    $c->debug('Removing an arbitrary file.');
+    $files = $c->finder($c->cwd)->files()->name('LICENSE');
+    foreach ($files as $file) {
+      $c->fs->remove($file->getRealPath());
+    }
+  }
+
+  public static function cleanup(CustomizeCommand $c): bool {
+    return TRUE;
+  }
+
+  public static function messages(CustomizeCommand $c): array {
+    return [
+      'title' => 'Greetings from the customizer for the "{{ package.name }}" project',
+    ];
+  }
+
+}
diff --git a/tests/phpunit/Fixtures/command/no_install_sub_dir/expected/composer.json b/tests/phpunit/Fixtures/no_install/expected/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/no_install_sub_dir/expected/composer.json
rename to tests/phpunit/Fixtures/no_install/expected/composer.json
index 6540581..c9da9a7 100644
--- a/tests/phpunit/Fixtures/command/no_install_sub_dir/expected/composer.json
+++ b/tests/phpunit/Fixtures/no_install/expected/composer.json
@@ -6,6 +6,5 @@
     "require": {
         "php": ">=8.2",
         "monolog/monolog": "^2.0"
-    },
-    "minimum-stability": "dev"
+    }
 }
diff --git a/tests/phpunit/Fixtures/command/no_install_sub_dir/base/composer.json b/tests/phpunit/Fixtures/no_install_sub_dir/base/composer.json
similarity index 100%
rename from tests/phpunit/Fixtures/command/no_install_sub_dir/base/composer.json
rename to tests/phpunit/Fixtures/no_install_sub_dir/base/composer.json
diff --git a/tests/phpunit/Fixtures/no_install_sub_dir/base/customize.php b/tests/phpunit/Fixtures/no_install_sub_dir/base/customize.php
new file mode 100644
index 0000000..50f6e2b
--- /dev/null
+++ b/tests/phpunit/Fixtures/no_install_sub_dir/base/customize.php
@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+use AlexSkrypnyk\Customizer\CustomizeCommand;
+
+/**
+ * Customizer configuration.
+ *
+ * phpcs:disable Drupal.Classes.ClassFileName.NoMatch
+ *
+ * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+ */
+class Customize {
+
+  public static function questions(CustomizeCommand $c): array {
+    return [
+      'Name' => [
+        'discover' => static function (CustomizeCommand $c): string {
+          $name = basename((string) getcwd());
+          $org = getenv('GITHUB_ORG') ?: 'acme';
+
+          return $org . '/' . $name;
+        },
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask('Package name', $discovered, static function (string $value): string {
+          if (!preg_match('/^[a-z0-9_.-]+\/[a-z0-9_.-]+$/', $value)) {
+            throw new \InvalidArgumentException(sprintf('The package name "%s" is invalid, it should be lowercase and have a vendor name, a forward slash, and a package name.', $value));
+          }
+
+          return $value;
+        }),
+      ],
+      'Description' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->ask(sprintf('Description for %s', $answers['Name'])),
+      ],
+      'License' => [
+        'question' => static fn(string $discovered, array $answers, CustomizeCommand $c): mixed => $c->io->choice('License type',
+          [
+            'MIT',
+            'GPL-3.0-or-later',
+            'Apache-2.0',
+          ],
+          empty($discovered) ? 'GPL-3.0-or-later' : $discovered
+        ),
+      ],
+    ];
+  }
+
+  public static function discoverLicense(CustomizeCommand $c): string {
+    return isset($c->composerjsonData['license']) && is_string($c->composerjsonData['license']) ? $c->composerjsonData['license'] : '';
+  }
+
+  public static function process(array $answers, CustomizeCommand $c): void {
+    $c->debug('Updating composer configuration');
+    $json = $c->readComposerJson($c->composerjson);
+    $json['name'] = $answers['Name'];
+    $json['description'] = $answers['Description'];
+    $json['license'] = $answers['License'];
+    $c->writeComposerJson($c->composerjson, $json);
+
+    $c->debug('Removing an arbitrary file.');
+    $files = $c->finder($c->cwd)->files()->name('LICENSE');
+    foreach ($files as $file) {
+      $c->fs->remove($file->getRealPath());
+    }
+  }
+
+  public static function cleanup(CustomizeCommand $c): bool {
+    if ($c->isComposerDependenciesInstalled) {
+      $c->debug('Add an example flag to composer.json.');
+      $json = $c->readComposerJson($c->composerjson);
+      $json['extra'] = is_array($json['extra']) ? $json['extra'] : [];
+      $json['extra']['customizer'] = TRUE;
+      $c->writeComposerJson($c->composerjson, $json);
+    }
+
+    return TRUE;
+  }
+
+}
diff --git a/tests/phpunit/Fixtures/command/install/expected/composer.json b/tests/phpunit/Fixtures/no_install_sub_dir/expected/composer.json
similarity index 83%
rename from tests/phpunit/Fixtures/command/install/expected/composer.json
rename to tests/phpunit/Fixtures/no_install_sub_dir/expected/composer.json
index 6540581..c9da9a7 100644
--- a/tests/phpunit/Fixtures/command/install/expected/composer.json
+++ b/tests/phpunit/Fixtures/no_install_sub_dir/expected/composer.json
@@ -6,6 +6,5 @@
     "require": {
         "php": ">=8.2",
         "monolog/monolog": "^2.0"
-    },
-    "minimum-stability": "dev"
+    }
 }
diff --git a/tests/phpunit/Functional/CreateProjectCommandInstallTest.php b/tests/phpunit/Functional/CreateProjectCommandInstallTest.php
index 0b3d385..3c0a485 100644
--- a/tests/phpunit/Functional/CreateProjectCommandInstallTest.php
+++ b/tests/phpunit/Functional/CreateProjectCommandInstallTest.php
@@ -13,82 +13,55 @@
  * Test Customizer as a single-file drop-in during `composer create-project`.
  */
 #[CoversClass(CustomizeCommand::class)]
-#[Group('command')]
-class CreateProjectCommandInstallTest extends CreateProjectCommandTestCase {
+#[Group('install')]
+class CreateProjectCommandInstallTest extends CustomizerTestCase {
 
-  #[Group('install')]
   #[RunInSeparateProcess]
   public function testInstall(): void {
-    $this->customizerSetAnswers([
+    static::customizerSetAnswers([
       'testorg/testpackage',
       'Test description',
       'MIT',
       self::TUI_ANSWER_NOTHING,
     ]);
 
-    $this->composerCreateProject();
+    $this->runComposerCreateProject();
 
-    $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
+    // Custom welcome message.
+    $this->assertComposerCommandSuccessOutputContains('Greetings from the customizer for the "yourorg/yourtempaltepackage" project',);
     $this->assertComposerCommandSuccessOutputContains('Project was customized');
-    $this->assertComposerLockUpToDate();
-    $this->assertFileEquals($this->dirs->fixtures . DIRECTORY_SEPARATOR . 'expected' . DIRECTORY_SEPARATOR . 'composer.json', $this->dirs->sut . DIRECTORY_SEPARATOR . 'composer.json');
-    $this->assertDirectoryExists($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor');
-    $this->assertDirectoryDoesNotExist($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR . 'alexskrypnyk/customizer');
-  }
 
-  #[Group('install')]
-  #[RunInSeparateProcess]
-  public function testInstallSubDir(): void {
-    $this->dirs->fs->mkdir($this->dirs->repo . DIRECTORY_SEPARATOR . 'src');
-    $this->dirs->fs->rename(
-      $this->dirs->repo . DIRECTORY_SEPARATOR . $this->customizerFile,
-      $this->dirs->repo . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . $this->customizerFile
-    );
-
-    $this->customizerSetAnswers([
-      'testorg/testpackage',
-      'Test description',
-      'MIT',
-      self::TUI_ANSWER_NOTHING,
-    ]);
-
-    $this->composerCreateProject();
-
-    $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
-    $this->assertComposerCommandSuccessOutputContains('Project was customized');
+    $this->assertFixtureDirectoriesEqual();
     $this->assertComposerLockUpToDate();
-    $this->assertFileEquals($this->dirs->fixtures . DIRECTORY_SEPARATOR . 'expected' . DIRECTORY_SEPARATOR . 'composer.json', $this->dirs->sut . DIRECTORY_SEPARATOR . 'composer.json');
-    $this->assertDirectoryExists($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor');
-    $this->assertDirectoryDoesNotExist($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR . 'alexskrypnyk/customizer');
   }
 
-  #[Group('install')]
   #[RunInSeparateProcess]
   public function testInstallAdditionalCleanup(): void {
-    $this->customizerSetAnswers([
+    static::customizerSetAnswers([
       'testorg/testpackage',
       'Test description',
       'MIT',
       self::TUI_ANSWER_NOTHING,
     ]);
 
-    $this->composerCreateProject();
+    $this->runComposerCreateProject();
 
     $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
     $this->assertComposerCommandSuccessOutputContains('Project was customized');
+
+    $this->assertFixtureDirectoriesEqual();
     $this->assertComposerLockUpToDate();
-    $this->assertFileEquals($this->dirs->fixtures . DIRECTORY_SEPARATOR . 'expected' . DIRECTORY_SEPARATOR . 'composer.json', $this->dirs->sut . DIRECTORY_SEPARATOR . 'composer.json');
   }
 
-  #[Group('install')]
   #[RunInSeparateProcess]
   public function testInstallNoConfigFile(): void {
-    $this->composerCreateProject();
+    $this->runComposerCreateProject();
+
+    $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
     $this->assertComposerCommandSuccessOutputContains('No questions were found. No changes were made');
+
+    $this->assertFixtureDirectoriesEqual();
     $this->assertComposerLockUpToDate();
-    $this->assertFileEquals($this->dirs->fixtures . DIRECTORY_SEPARATOR . 'expected' . DIRECTORY_SEPARATOR . 'composer.json', $this->dirs->sut . DIRECTORY_SEPARATOR . 'composer.json');
-    $this->assertDirectoryExists($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor');
-    $this->assertDirectoryExists($this->dirs->sut . DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR . 'alexskrypnyk/customizer');
   }
 
 }
diff --git a/tests/phpunit/Functional/CreateProjectCommandNoInstallTest.php b/tests/phpunit/Functional/CreateProjectCommandNoInstallTest.php
index e389913..68df937 100644
--- a/tests/phpunit/Functional/CreateProjectCommandNoInstallTest.php
+++ b/tests/phpunit/Functional/CreateProjectCommandNoInstallTest.php
@@ -13,8 +13,8 @@
  * Test Customizer using `composer create-project --no-install`.
  */
 #[CoversClass(CustomizeCommand::class)]
-#[Group('command')]
-class CreateProjectCommandNoInstallTest extends CreateProjectCommandTestCase {
+#[Group('no-install')]
+class CreateProjectCommandNoInstallTest extends CustomizerTestCase {
 
   /**
    * {@inheritdoc}
@@ -23,59 +23,57 @@ protected function setUp(): void {
     parent::setUp();
     // Update the 'autoload' to include the command file from the project
     // root to get code test coverage.
-    $json = CustomizeCommand::readComposerJson($this->dirs->repo . '/composer.json');
+    $json = CustomizeCommand::readComposerJson(static::$repo . '/composer.json');
     $json['autoload'] = is_array($json['autoload']) ? $json['autoload'] : [];
-    $json['autoload']['classmap'] = [$this->dirs->root . DIRECTORY_SEPARATOR . $this->customizerFile];
-    CustomizeCommand::writeComposerJson($this->dirs->repo . '/composer.json', $json);
+    $json['autoload']['classmap'] = [static::$root . DIRECTORY_SEPARATOR . 'CustomizeCommand.php'];
+    CustomizeCommand::writeComposerJson(static::$repo . '/composer.json', $json);
   }
 
-  #[Group('no-install')]
-  #[Group('smoke')]
   #[RunInSeparateProcess]
   public function testNoInstall(): void {
-    $this->customizerSetAnswers([
+    CustomizerTestCase::customizerSetAnswers([
       'testorg/testpackage',
       'Test description',
       'MIT',
       self::TUI_ANSWER_NOTHING,
     ]);
 
-    $this->composerCreateProject(['--no-install' => TRUE]);
+    $this->runComposerCreateProject(['--no-install' => TRUE]);
 
-    $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
+    // Custom welcome message.
+    $this->assertComposerCommandSuccessOutputContains('Greetings from the customizer for the "yourorg/yourtempaltepackage" project',);
     $this->assertComposerCommandSuccessOutputContains('Project was customized');
 
-    $this->assertFixtureFiles();
+    $this->assertFixtureDirectoriesEqual();
   }
 
   #[RunInSeparateProcess]
-  #[Group('no-install')]
   public function testNoInstallSubDir(): void {
     // Move the command stub pre-created in setUp() to the 'src' directory.
-    $this->dirs->fs->mkdir($this->dirs->repo . DIRECTORY_SEPARATOR . 'src');
-    $this->dirs->fs->rename(
-      $this->dirs->repo . DIRECTORY_SEPARATOR . $this->customizerFile,
-      $this->dirs->repo . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . $this->customizerFile
+    $this->fs->mkdir(static::$repo . DIRECTORY_SEPARATOR . 'src');
+    $this->fs->rename(
+      static::$repo . DIRECTORY_SEPARATOR . 'CustomizeCommand.php',
+      static::$repo . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . 'CustomizeCommand.php'
     );
 
-    $json = CustomizeCommand::readComposerJson($this->dirs->repo . DIRECTORY_SEPARATOR . 'composer.json');
+    $json = CustomizeCommand::readComposerJson(static::$repo . DIRECTORY_SEPARATOR . 'composer.json');
     $json['autoload'] = is_array($json['autoload']) ? $json['autoload'] : [];
-    $json['autoload']['classmap'] = ['src/' . $this->customizerFile];
-    CustomizeCommand::writeComposerJson($this->dirs->repo . DIRECTORY_SEPARATOR . 'composer.json', $json);
+    $json['autoload']['classmap'] = ['src/CustomizeCommand.php'];
+    CustomizeCommand::writeComposerJson(static::$repo . DIRECTORY_SEPARATOR . 'composer.json', $json);
 
-    $this->customizerSetAnswers([
+    CustomizerTestCase::customizerSetAnswers([
       'testorg/testpackage',
       'Test description',
       'MIT',
       self::TUI_ANSWER_NOTHING,
     ]);
 
-    $this->composerCreateProject(['--no-install' => TRUE]);
+    $this->runComposerCreateProject(['--no-install' => TRUE]);
 
     $this->assertComposerCommandSuccessOutputContains('Welcome to the "yourorg/yourtempaltepackage" project customizer');
     $this->assertComposerCommandSuccessOutputContains('Project was customized');
 
-    $this->assertFixtureFiles();
+    $this->assertFixtureDirectoriesEqual();
   }
 
 }
diff --git a/tests/phpunit/Functional/CreateProjectCommandTestCase.php b/tests/phpunit/Functional/CreateProjectCommandTestCase.php
deleted file mode 100644
index 44dbf86..0000000
--- a/tests/phpunit/Functional/CreateProjectCommandTestCase.php
+++ /dev/null
@@ -1,65 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests\Functional;
-
-use AlexSkrypnyk\Customizer\CustomizeCommand;
-use AlexSkrypnyk\Customizer\Tests\Dirs;
-use PHPUnit\Framework\Attributes\CoversClass;
-use PHPUnit\Framework\Attributes\Group;
-
-/**
- * Base class for functional project command tests.
- */
-#[CoversClass(CustomizeCommand::class)]
-#[Group('command')]
-class CreateProjectCommandTestCase extends CustomizerTestCase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected static string $composerJsonFile = 'tests/phpunit/Fixtures/command/composer.json';
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp(): void {
-    $test_name = $this->name();
-
-    $reflector = new \ReflectionClass(CustomizeCommand::class);
-    $this->customizerFile = basename((string) $reflector->getFileName());
-
-    // Initialize the Composer command tester.
-    $this->composerCommandInit();
-
-    // Initialize the directories.
-    $this->dirsInit(function (Dirs $dirs) use ($test_name): void {
-      $this->dirs->fixtures .= DIRECTORY_SEPARATOR . 'command' . DIRECTORY_SEPARATOR . static::toFixtureDirName($test_name);
-      if (!is_dir($this->dirs->fixtures)) {
-        throw new \RuntimeException('The fixtures directory does not exist: ' . $this->dirs->fixtures);
-      }
-
-      $dirs->fs->mirror(
-        $this->dirs->fixtures . DIRECTORY_SEPARATOR . 'base',
-        $dirs->repo
-      );
-
-      // Create an empty command file in the 'system under test' to replicate a
-      // real scenario during test where the file is manually copied into a real
-      // project and then removed by the command after customization runs.
-      $dirs->fs->touch($dirs->repo . DIRECTORY_SEPARATOR . $this->customizerFile);
-    });
-
-    // Update the 'autoload' to include the command file from the project
-    // root to get code test coverage.
-    $json = CustomizeCommand::readComposerJson($this->dirs->repo . '/composer.json');
-
-    // Save the test package name for later use in tests.
-    $this->packageName = is_string($json['name']) ? $json['name'] : '';
-
-    // Change the current working directory to the 'system under test'.
-    chdir($this->dirs->sut);
-  }
-
-}
diff --git a/tests/phpunit/Functional/CustomizerTestCase.php b/tests/phpunit/Functional/CustomizerTestCase.php
index e880000..0b4ca5f 100644
--- a/tests/phpunit/Functional/CustomizerTestCase.php
+++ b/tests/phpunit/Functional/CustomizerTestCase.php
@@ -5,43 +5,83 @@
 namespace AlexSkrypnyk\Customizer\Tests\Functional;
 
 use AlexSkrypnyk\Customizer\CustomizeCommand;
-use AlexSkrypnyk\Customizer\Tests\Dirs;
-use AlexSkrypnyk\Customizer\Tests\Traits\CmdTrait;
-use AlexSkrypnyk\Customizer\Tests\Traits\ComposerTrait;
-use AlexSkrypnyk\Customizer\Tests\Traits\DirsTrait;
+use Composer\Console\Application;
+use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\TestCase;
 use PHPUnit\Framework\TestStatus\Error;
 use PHPUnit\Framework\TestStatus\Failure;
+use Symfony\Component\Console\Tester\ApplicationTester;
+use Symfony\Component\Filesystem\Filesystem;
 use Symfony\Component\Finder\Finder;
+use Symfony\Component\Process\Process;
 
 /**
  * Base class for functional tests.
+ *
+ * This class is intended to be distributed with the Customizer package and
+ * used in consumer site's tests to allow easy testing of the integrated
+ * Customizer command.
+ *
+ * Extend this class in your test case to get access to the Customizer command
+ * test runner and the necessary helper methods.
  */
 class CustomizerTestCase extends TestCase {
 
-  use ComposerTrait;
-  use DirsTrait;
-  use CmdTrait;
-
   /**
    * TUI answer to indicate that the user did not provide any input.
    */
   const TUI_ANSWER_NOTHING = 'NOTHING';
 
+  /**
+   * Path to the fixtures directory from the repository root.
+   */
+  const FIXTURES_DIR = 'tests/phpunit/Fixtures';
+
+  /**
+   * Path to the root directory of this project.
+   */
+  protected static string $root;
+
+  /**
+   * Path to the fixtures directory from the root of this project.
+   */
+  protected static string $fixtures;
+
+  /**
+   * Main build directory where the rest of the directories located.
+   *
+   * The "build" in this context is a place to store assets produced by a single
+   * test run.
+   */
+  protected static string $build;
+
+  /**
+   * Directory used as a source in the operations.
+   *
+   * Could be a copy of the current repository with custom adjustments or a
+   * fixture repository.
+   */
+  protected static string $repo;
+
+  /**
+   * Directory where the test will run.
+   */
+  protected static string $sut;
+
   /**
    * The source package name used in tests.
    */
   protected string $packageName;
 
   /**
-   * The Customizer file name.
+   * The application tester.
    */
-  protected string $customizerFile;
+  protected ApplicationTester $tester;
 
   /**
-   * The Composer JSON file name.
+   * The file system.
    */
-  protected static string $composerJsonFile = 'composer.json';
+  protected Filesystem $fs;
 
   /**
    * {@inheritdoc}
@@ -49,48 +89,131 @@ class CustomizerTestCase extends TestCase {
   protected function setUp(): void {
     parent::setUp();
 
-    if (!isset(static::$composerJsonFile)) {
-      throw new \RuntimeException('The $composerJsonFile property must be set in the child class.');
-    }
-
-    $reflector = new \ReflectionClass(CustomizeCommand::class);
-    $this->customizerFile = basename((string) $reflector->getFileName());
-
-    // Initialize the Composer command tester.
-    $this->composerCommandInit();
+    $this->initComposerTester();
 
-    $this->dirsInit(static function (Dirs $dirs): void {
-      $dirs->fs->copy($dirs->root . DIRECTORY_SEPARATOR . static::$composerJsonFile, $dirs->repo . '/composer.json');
-      // Copy the configuration file.
-      $dirs->fs->copy($dirs->root . DIRECTORY_SEPARATOR . CustomizeCommand::CONFIG_FILE, $dirs->repo . DIRECTORY_SEPARATOR . CustomizeCommand::CONFIG_FILE);
-    }, (string) getcwd());
+    $this->initLocations((string) getcwd());
 
-    // Projects using this project through a plugin need to have this
+    // Projects using this project through a plugin must have this
     // repository added to their composer.json to be able to download it
     // during the test.
-    $json = CustomizeCommand::readComposerJson($this->dirs->repo . '/composer.json');
+    $json = CustomizeCommand::readComposerJson(static::$repo . '/composer.json');
+    $json['minimum-stability'] = 'dev';
     $json['repositories'] = [
       [
         'type' => 'path',
-        'url' => $this->dirs->root,
+        'url' => static::$root,
         'options' => ['symlink' => TRUE],
       ],
     ];
-    CustomizeCommand::writeComposerJson($this->dirs->repo . '/composer.json', $json);
+    CustomizeCommand::writeComposerJson(static::$repo . '/composer.json', $json);
 
     // Save the package name for later use in tests.
     $this->packageName = is_string($json['name']) ? $json['name'] : '';
 
     // Change the current working directory to the 'system under test'.
-    chdir($this->dirs->sut);
+    chdir(static::$sut);
+  }
+
+  /**
+   * Initialize the Composer command tester.
+   */
+  protected function initComposerTester(): void {
+    $application = new Application();
+    $application->setAutoExit(FALSE);
+    $application->setCatchExceptions(FALSE);
+    if (method_exists($application, 'setCatchErrors')) {
+      $application->setCatchErrors(FALSE);
+    }
+
+    $this->tester = new ApplicationTester($application);
+
+    // Composer autoload uses per-project Composer binary, if the
+    // `composer/composer` is included in the project as a dependency.
+    //
+    // When the test runs and creates SUT, the Composer binary used is
+    // from the SUT's `vendor` directory. The Customizer may remove the
+    // `vendor/composer/composer` directory as a part of the cleanup, resulting
+    // in the Composer autoloader having an empty path to the Composer binary.
+    //
+    // This is extremely difficult to debug, because there is no clear error
+    // message apart from `Could not open input file`.
+    //
+    // To prevent this, we set the `COMPOSER_BINARY` environment variable to the
+    // Composer binary path found in the system.
+    // @see \Composer\EventDispatcher::doDispatch().
+    $composer_bin = shell_exec(escapeshellcmd('which composer'));
+    if ($composer_bin === FALSE) {
+      throw new \RuntimeException('Composer binary not found');
+    }
+    putenv('COMPOSER_BINARY=' . trim((string) $composer_bin));
+  }
+
+  /**
+   * Initialize the locations.
+   *
+   * @param string $cwd
+   *   The current working directory.
+   * @param callable|null $cb
+   *   Callback to run after initialization.
+   */
+  protected function initLocations(string $cwd, ?callable $cb = NULL): void {
+    $this->fs = new Filesystem();
+
+    static::$root = (string) realpath($cwd);
+    if (!is_dir(static::$root)) {
+      throw new \RuntimeException('The repository root directory does not exist: ' . static::$root);
+    }
+
+    static::$fixtures = static::$root . DIRECTORY_SEPARATOR . static::FIXTURES_DIR;
+    if (!is_dir(static::$fixtures)) {
+      throw new \RuntimeException('The fixtures directory does not exist: ' . static::$fixtures);
+    }
+
+    static::$build = rtrim(sys_get_temp_dir(), DIRECTORY_SEPARATOR) . DIRECTORY_SEPARATOR . 'customizer-' . microtime(TRUE);
+    static::$sut = static::$build . '/sut';
+    static::$repo = static::$build . '/local_repo';
+
+    $this->fs->mkdir(static::$build);
+    $this->fs->mkdir(static::$sut);
+    $this->fs->mkdir(static::$repo);
+
+    // Set the fixtures directory based on the test name.
+    $fixture_dir = $this->name();
+    $fixture_dir = str_contains($fixture_dir, '::') ? explode('::', $fixture_dir)[1] : $fixture_dir;
+    $fixture_dir = strtolower((string) preg_replace('/(?<!^)[A-Z]/', '_$0', $fixture_dir));
+    $fixture_dir = str_replace('test_', '', $fixture_dir);
+    static::$fixtures .= DIRECTORY_SEPARATOR . $fixture_dir;
+
+    // Further adjust the fixtures directory name if the test uses a
+    // data provider with named data sets.
+    if ($this->usesDataProvider() && !empty($this->dataName())) {
+      static::$fixtures .= DIRECTORY_SEPARATOR . $this->dataName();
+    }
+
+    // Copy the 'base' fixture files to the repository if they were provided for
+    // this test.
+    if (is_dir(static::$fixtures)) {
+      $this->fs->mirror(static::$fixtures . DIRECTORY_SEPARATOR . 'base', static::$repo);
+    }
+
+    // Create an empty command file in the 'system under test' to replicate a
+    // real scenario during test where the file is manually copied into a real
+    // project and then removed by the command after customization runs.
+    $this->fs->touch(static::$repo . DIRECTORY_SEPARATOR . 'CustomizeCommand.php');
+
+    if ($cb !== NULL && is_callable($cb) && $cb instanceof \Closure) {
+      // @phpstan-ignore-next-line
+      \Closure::bind($cb, $this, self::class)();
+    }
   }
 
   /**
    * {@inheritdoc}
    */
   protected function tearDown(): void {
-    if (!$this->hasFailed()) {
-      $this->dirsClean();
+    // Clean up the directories if the test passed.
+    if (!$this->status() instanceof Failure && !$this->status() instanceof Error) {
+      $this->fs->remove(static::$build);
     }
 
     parent::tearDown();
@@ -100,26 +223,56 @@ protected function tearDown(): void {
    * {@inheritdoc}
    */
   protected function onNotSuccessfulTest(\Throwable $t): never {
-    fwrite(STDERR, 'see below' . PHP_EOL . PHP_EOL . $this->dirsInfo() . PHP_EOL . $t->getMessage() . PHP_EOL);
+    // Print the locations information and the exception message.
+    $lines[] = '-- LOCATIONS --';
+    $lines[] = 'Root       : ' . static::$root;
+    $lines[] = 'Fixtures   : ' . static::$fixtures;
+    $lines[] = 'Build      : ' . static::$build;
+    $lines[] = 'Local repo : ' . static::$repo;
+    $lines[] = 'SUT        : ' . static::$sut;
+    $info = implode(PHP_EOL, $lines) . PHP_EOL;
+
+    fwrite(STDERR, 'see below' . PHP_EOL . PHP_EOL . $info . PHP_EOL . $t->getMessage() . PHP_EOL);
 
     parent::onNotSuccessfulTest($t);
   }
 
   /**
-   * Check if the test has failed.
+   * Run an arbitrary command.
+   *
+   * @param string $cmd
+   *   The command to execute (escaped as required)
+   * @param string $cwd
+   *   The current working directory to run the command from.
+   * @param array $env
+   *   Environment variables to define for the subprocess.
    *
-   * @return bool
-   *   TRUE if the test has failed, FALSE otherwise.
+   * @return string
+   *   Standard output from the command
    */
-  public function hasFailed(): bool {
-    $status = $this->status();
+  protected static function runCmd(string $cmd, ?string $cwd, array $env = []): string {
+    $env += $env + ['PATH' => getenv('PATH'), 'HOME' => getenv('HOME')];
+
+    $process = Process::fromShellCommandline($cmd, $cwd, $env);
+    $process->setTimeout(300)->setIdleTimeout(300)->run();
+
+    $code = $process->getExitCode();
+    if (0 != $code) {
+      throw new \RuntimeException("Exit code: {$code}\n\n" . $process->getErrorOutput() . "\n\n" . $process->getOutput());
+    }
 
-    return $status instanceof Failure || $status instanceof Error;
+    return $process->getOutput();
   }
 
-  protected function customizerSetAnswers(array $answers): void {
+  /**
+   * Set the answers for the Customizer TUI.
+   *
+   * @param array $answers
+   *   The answers to set.
+   */
+  protected static function customizerSetAnswers(array $answers): void {
     foreach ($answers as $key => $answer) {
-      if ($answer === self::TUI_ANSWER_NOTHING) {
+      if ($answer === static::TUI_ANSWER_NOTHING) {
         $answers[$key] = "\n";
       }
     }
@@ -127,16 +280,22 @@ protected function customizerSetAnswers(array $answers): void {
     putenv('CUSTOMIZER_ANSWERS=' . json_encode($answers));
   }
 
-  protected function composerCreateProject(array $options = []): void {
+  /**
+   * Run the `composer create-project` command with the given options.
+   *
+   * @param array<string,string|bool|array<mixed,mixed>> $options
+   *   The command options.
+   */
+  protected function runComposerCreateProject(array $options = []): void {
     $defaults = [
       'command' => 'create-project',
       'package' => $this->packageName,
-      'directory' => $this->dirs->sut,
+      'directory' => static::$sut,
       'version' => '@dev',
       '--repository' => [
         json_encode([
           'type' => 'path',
-          'url' => $this->dirs->repo,
+          'url' => static::$repo,
           'options' => ['symlink' => FALSE],
         ]),
       ],
@@ -145,87 +304,296 @@ protected function composerCreateProject(array $options = []): void {
     $this->tester->run($options + $defaults);
   }
 
+  /**
+   * Assert that the Composer lock file is up to date.
+   */
   protected function assertComposerLockUpToDate(): void {
+    if (!empty(getenv('UPDATE_TEST_FIXTURES'))) {
+      return;
+    }
+
     $this->assertFileExists('composer.lock');
 
-    $this->cmdRun('composer validate', $this->dirs->sut);
+    static::runCmd('composer validate', static::$sut);
   }
 
   /**
-   * Assert that the fixture files match the actual files.
+   * Assert that the Composer JSON files match.
    *
-   * @param array<int,string> $exclude
-   *   The list of files to exclude.
+   * @param string $expected
+   *   The expected file.
+   * @param string $actual
+   *   The actual file.
    */
-  protected function assertFixtureFiles(array $exclude = []): void {
-    $expected = $this->dirs->fixtures . '/expected';
-    $actual = $this->dirs->sut;
-
-    if (!empty(getenv('UPDATE_TEST_FIXTURES'))) {
-      $this->dirs->fs->remove($expected);
+  protected function assertComposerJsonFilesEqual(string $expected, string $actual): void {
+    $this->assertFileExists($expected);
+    $this->assertFileExists($actual);
 
-      $finder = new Finder();
-      $finder
-        ->ignoreDotFiles(FALSE)
-        ->ignoreVCS(TRUE)
-        ->files()
-        ->exclude($exclude)
-        ->in($actual);
+    $expected = json_decode((string) file_get_contents($expected), TRUE);
 
-      $this->dirs->fs->mirror($actual, $expected, $finder->getIterator());
+    // Remove test data.
+    $data = json_decode((string) file_get_contents($actual), TRUE);
+    if (!is_array($data)) {
+      $this->fail('The actual file is not a valid JSON file.');
+    }
+    unset($data['minimum-stability']);
+    foreach ($data['repositories'] as $key => $repository) {
+      if ($repository['type'] === 'path' && $repository['url'] === static::$root) {
+        unset($data['repositories'][$key]);
+      }
     }
-    else {
-      $this->assertDirsEqual($expected, $actual, $exclude);
+    if (empty($data['repositories'])) {
+      unset($data['repositories']);
     }
+    file_put_contents($actual, json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . PHP_EOL);
+
+    $this->assertSame($expected, $actual);
   }
 
   /**
-   * Compare directories.
+   * Assert successful Composer command output contains the expected strings.
    *
-   * @param string $expected
-   *   The expected directory.
-   * @param string $actual
-   *   The actual directory.
-   * @param array<int,string> $exclude
-   *   The list of files to exclude.
-   */
-  protected function assertDirsEqual(string $expected, string $actual, array $exclude = []): void {
-    $finder_expected = new Finder();
-    $finder_expected
-      ->ignoreDotFiles(FALSE)
-      ->ignoreVCS(TRUE)
-      ->exclude($exclude)
-      ->files()
-      ->in($expected);
-
-    $finder_actual = new Finder();
-    $finder_actual
-      ->ignoreDotFiles(FALSE)
-      ->ignoreVCS(TRUE)
-      ->exclude($exclude)
-      ->files()
-      ->in($actual);
-
-    // Check that all files in expected are present in actual and are equal.
-    foreach ($finder_expected as $file) {
-      $this->assertFileExists($actual . '/' . $file->getRelativePathname());
-      $this->assertFileEquals($file->getPathname(), $actual . '/' . $file->getRelativePathname());
-    }
-
-    // Check that there are no unexpected files in actual.
-    foreach ($finder_actual as $file) {
-      $this->assertFileExists($expected . '/' . $file->getRelativePathname(), 'Unexpected file found: ' . $file->getRelativePathname());
+   * @param string|array $strings
+   *   The expected strings.
+   */
+  protected function assertComposerCommandSuccessOutputContains(string|array $strings): void {
+    $strings = is_array($strings) ? $strings : [$strings];
+
+    if ($this->tester->getStatusCode() !== 0) {
+      $this->fail($this->tester->getDisplay());
+    }
+    $this->assertSame(0, $this->tester->getStatusCode(), sprintf("The Composer command should have completed successfully:\n%s", $this->tester->getInput()->__toString()));
+
+    $output = $this->tester->getDisplay(TRUE);
+    foreach ($strings as $string) {
+      $this->assertStringContainsString($string, $output);
     }
   }
 
   /**
-   * Convert a test name to a fixture directory name.
+   * Assert that fixtures directories are equal.
    */
-  protected static function toFixtureDirName(string $name): string {
-    $name = str_contains($name, '::') ? explode('::', $name)[1] : $name;
-    $name = strtolower((string) preg_replace('/(?<!^)[A-Z]/', '_$0', $name));
+  protected function assertFixtureDirectoriesEqual(): void {
+    $this->assertDirectoriesEqual(static::$fixtures . DIRECTORY_SEPARATOR . 'expected', static::$sut);
+  }
+
+  /**
+   * Assert that 2 directories have the same files and content, ignoring some.
+   *
+   * The main purpose of this method is to allow to create before/after file
+   * structures and compare them, ignoring some files or content changes. This
+   * allows to create fixture hierarchies fast.
+   *
+   * The first directory could be updated using the files from the second
+   * directory if the environment variable `UPDATE_TEST_FIXTURES` is set.
+   * This is useful to update the fixtures after the changes in the code.
+   *
+   * Files can be excluded from the comparison completely or only checked for
+   * presence and ignored for the content changes using a .gitignore-like
+   * file `.ignorecontent` that can be placed in the second directory.
+   *
+   * The syntax for the file is similar to .gitignore with addition of
+   * the content ignoring using ^ prefix:
+   * Comments start with #.
+   * file    Ignore file.
+   * dir/    Ignore directory and all subdirectories.
+   * dir/*   Ignore all files in directory, but not subdirectories.
+   * ^file   Ignore content changes in file, but not the file itself.
+   * ^dir/   Ignore content changes in all files and subdirectories, but check
+   *         that the directory itself exists.
+   * ^dir/*  Ignore content changes in all files, but not subdirectories and
+   *         check that the directory itself exists.
+   * !file   Do not ignore file.
+   * !dir/   Do not ignore directory, including all subdirectories.
+   * !dir/*  Do not ignore all files in directory, but not subdirectories.
+   * !^file  Do not ignore content changes in file.
+   * !^dir/  Do not ignore content changes in all files and subdirectories.
+   * !^dir/* Do not ignore content changes in all files, but not subdirectories.
+   *
+   * This assertion method is deliberately used as a single assertion for
+   * portability.
+   *
+   * @param string $dir1
+   *   The first directory.
+   * @param string $dir2
+   *   The second directory.
+   *
+   * @throws \PHPUnit\Framework\AssertionFailedError
+   *   If the directories are not equal.
+   */
+  protected function assertDirectoriesEqual(string $dir1, string $dir2): void {
+    $rules_file = $dir1 . DIRECTORY_SEPARATOR . '.ignorecontent';
+
+    // Initialize the rules arrays: skip, presence, include, and global.
+    $rules = ['skip' => ['.ignorecontent'], 'content' => [], 'include' => [], 'global' => []];
+
+    // Parse the .ignorecontent file.
+    if (file_exists($rules_file)) {
+      $lines = file($rules_file, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+
+      if ($lines === FALSE) {
+        throw new \RuntimeException('Failed to read the .ignorecontent file.');
+      }
+
+      foreach ($lines as $line) {
+        $line = trim($line);
+        if ($line[0] === '#') {
+          continue;
+        }
+        elseif ($line[0] === '!') {
+          $rules['include'][] = $line[1] === '^' ? substr($line, 2) : substr($line, 1);
+        }
+        elseif ($line[0] === '^') {
+          $rules['content'][] = substr($line, 1);
+        }
+        elseif (!str_contains($line, DIRECTORY_SEPARATOR)) {
+          // Treat patterns without slashes as global patterns.
+          $rules['global'][] = $line;
+        }
+        else {
+          // Regular skip rule.
+          $rules['skip'][] = $line;
+        }
+      }
+    }
+
+    // Match paths.
+    $match_path = static function (string $path, string $pattern, bool $is_directory): bool {
+      $path .= $is_directory ? DIRECTORY_SEPARATOR : '';
+      // Match directory pattern (e.g., "dir/").
+      if (str_ends_with($pattern, DIRECTORY_SEPARATOR)) {
+        return str_starts_with($path, rtrim($pattern, DIRECTORY_SEPARATOR));
+      }
+      // Match direct children (e.g., "dir/*").
+      if (str_contains($pattern, '/*')) {
+        $parent_dir = rtrim($pattern, '/*') . DIRECTORY_SEPARATOR;
+
+        return str_starts_with($path, $parent_dir) && substr_count($path, DIRECTORY_SEPARATOR) === substr_count($parent_dir, DIRECTORY_SEPARATOR);
+      }
+
+      // @phpcs:ignore Drupal.Functions.DiscouragedFunctions.Discouraged
+      return fnmatch($pattern, $path);
+    };
+
+    // Get the files in the directories.
+    $get_files = static function (string $dir, array $rules, callable $match_path): array {
+      $files = [];
+      $iterator = new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator($dir, \FilesystemIterator::SKIP_DOTS));
+      foreach ($iterator as $file) {
+        if (!$file instanceof \SplFileInfo) {
+          continue;
+        }
+
+        $is_directory = $file->isDir();
+        $path = str_replace($dir . DIRECTORY_SEPARATOR, '', $file->getPathname());
+        $path .= $is_directory ? DIRECTORY_SEPARATOR : '';
+
+        foreach ($rules['global'] as $pattern) {
+          if ($match_path(basename($path), $pattern, $is_directory)) {
+            continue 2;
+          }
+        }
+
+        $is_included = FALSE;
+        foreach ($rules['include'] as $pattern) {
+          if ($match_path($path, $pattern, $is_directory)) {
+            $is_included = TRUE;
+            break;
+          }
+        }
+
+        if (!$is_included) {
+          foreach ($rules['skip'] as $pattern) {
+            if ($match_path($path, $pattern, $is_directory)) {
+              continue 2;
+            }
+          }
+        }
+
+        $is_content = FALSE;
+        if (!$is_included) {
+          foreach ($rules['content'] as $pattern) {
+            if ($match_path($path, $pattern, $is_directory)) {
+              $is_content = TRUE;
+              break;
+            }
+          }
+        }
+
+        if ($is_content) {
+          $files[$path] = 'content';
+        }
+        else {
+          $files[$path] = $is_directory ? 'content' : md5_file($file->getPathname());
+        }
+      }
+      ksort($files);
+
+      return $files;
+    };
+
+    $dir1_files = $get_files($dir1, $rules, $match_path);
+    $dir2_files = $get_files($dir2, $rules, $match_path);
+
+    // Allow updating the test fixtures.
+    if (getenv('UPDATE_TEST_FIXTURES')) {
+      $allowed_files = array_keys($dir2_files);
+      $finder = new Finder();
+      $finder->files()->in($dir2)->filter(static function (\SplFileInfo $file) use ($allowed_files, $dir2): bool {
+        $relativePath = str_replace($dir2 . DIRECTORY_SEPARATOR, '', $file->getRealPath());
+
+        return in_array($relativePath, $allowed_files);
+      });
+
+      $this->fs->mirror($dir2, $dir1, $finder->getIterator(), [
+        'override' => TRUE,
+      ]);
+
+      return;
+    }
+
+    $diffs = [
+      'only_in_dir1' => array_diff_key($dir1_files, $dir2_files),
+      'only_in_dir2' => array_diff_key($dir2_files, $dir1_files),
+      'different_files' => [],
+    ];
+
+    // Compare files where content is not ignored.
+    foreach ($dir1_files as $file => $hash) {
+      if (isset($dir2_files[$file]) && $hash !== $dir2_files[$file] && !in_array($file, $rules['content'])) {
+        $diffs['different_files'][] = $file;
+      }
+    }
+
+    // If differences exist, throw assertion error.
+    if (!empty($diffs['only_in_dir1']) || !empty($diffs['only_in_dir2']) || !empty($diffs['different_files'])) {
+      $message = "Differences between directories:\n";
+
+      if (!empty($diffs['only_in_dir1'])) {
+        $message .= "Files only in dir1:\n";
+        foreach (array_keys($diffs['only_in_dir1']) as $file) {
+          $message .= sprintf('  %s%s', $file, PHP_EOL);
+        }
+      }
+
+      if (!empty($diffs['only_in_dir2'])) {
+        $message .= "Files only in dir2:\n";
+        foreach (array_keys($diffs['only_in_dir2']) as $file) {
+          $message .= sprintf('  %s%s', $file, PHP_EOL);
+        }
+      }
+
+      if (!empty($diffs['different_files'])) {
+        $message .= "Files that differ in content:\n";
+        foreach ($diffs['different_files'] as $file) {
+          $message .= sprintf('  %s%s', $file, PHP_EOL);
+        }
+      }
+
+      throw new AssertionFailedError($message);
+    }
 
-    return str_replace('test_', '', $name);
+    $this->assertTrue(TRUE);
   }
 
 }
diff --git a/tests/phpunit/Traits/CmdTrait.php b/tests/phpunit/Traits/CmdTrait.php
deleted file mode 100644
index b0f38db..0000000
--- a/tests/phpunit/Traits/CmdTrait.php
+++ /dev/null
@@ -1,43 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests\Traits;
-
-use Symfony\Component\Process\Process;
-
-/**
- * Trait CmdTrait.
- *
- * Provides methods for running arbitrary commands.
- */
-trait CmdTrait {
-
-  /**
-   * Runs an arbitrary command.
-   *
-   * @param string $cmd
-   *   The command to execute (escaped as required)
-   * @param string $cwd
-   *   The current working directory to run the command from.
-   * @param array $env
-   *   Environment variables to define for the subprocess.
-   *
-   * @return string
-   *   Standard output from the command
-   */
-  protected function cmdRun($cmd, $cwd, array $env = []): string {
-    $env += $env + ['PATH' => getenv('PATH'), 'HOME' => getenv('HOME')];
-
-    $process = Process::fromShellCommandline($cmd, $cwd, $env);
-    $process->setTimeout(300)->setIdleTimeout(300)->run();
-
-    $exitCode = $process->getExitCode();
-    if (0 != $exitCode) {
-      throw new \RuntimeException("Exit code: {$exitCode}\n\n" . $process->getErrorOutput() . "\n\n" . $process->getOutput());
-    }
-
-    return $process->getOutput();
-  }
-
-}
diff --git a/tests/phpunit/Traits/ComposerTrait.php b/tests/phpunit/Traits/ComposerTrait.php
deleted file mode 100644
index 9e3e05a..0000000
--- a/tests/phpunit/Traits/ComposerTrait.php
+++ /dev/null
@@ -1,67 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests\Traits;
-
-use Composer\Console\Application;
-use Symfony\Component\Console\Tester\ApplicationTester;
-
-/**
- * Trait ComposerCommandTrait.
- *
- * Provides methods for working with Composer.
- */
-trait ComposerTrait {
-
-  /**
-   * The application tester.
-   */
-  protected ApplicationTester $tester;
-
-  protected function composerCommandInit(): void {
-    $application = new Application();
-    $application->setAutoExit(FALSE);
-    $application->setCatchExceptions(FALSE);
-    if (method_exists($application, 'setCatchErrors')) {
-      $application->setCatchErrors(FALSE);
-    }
-
-    $this->tester = new ApplicationTester($application);
-
-    // Composer autoload uses per-project Composer binary, if the
-    // `composer/composer` is included in the project as a dependency.
-    //
-    // When the test runs and creates SUT, the Composer binary used is
-    // from the SUT's `vendor` directory. The Customizer may remove the
-    // `vendor/composer/composer` directory as a part of the cleanup, resulting
-    // in the Composer autoloader having an empty path to the Composer binary.
-    //
-    // This is extremely difficult to debug, because there is no clear error
-    // message apart from `Could not open input file`.
-    //
-    // To prevent this, we set the `COMPOSER_BINARY` environment variable to the
-    // Composer binary path found in the system.
-    // @see \Composer\EventDispatcher::doDispatch().
-    $composer_bin = shell_exec(escapeshellcmd('which composer'));
-    if ($composer_bin === FALSE) {
-      throw new \RuntimeException('Composer binary not found');
-    }
-    putenv('COMPOSER_BINARY=' . trim((string) $composer_bin));
-  }
-
-  protected function assertComposerCommandSuccessOutputContains(string|array $strings): void {
-    $strings = is_array($strings) ? $strings : [$strings];
-
-    if ($this->tester->getStatusCode() !== 0) {
-      $this->fail($this->tester->getDisplay());
-    }
-    $this->assertSame(0, $this->tester->getStatusCode(), sprintf("The Composer command should have completed successfully:\n%s", $this->tester->getInput()->__toString()));
-
-    $output = $this->tester->getDisplay(TRUE);
-    foreach ($strings as $string) {
-      $this->assertStringContainsString($string, $output);
-    }
-  }
-
-}
diff --git a/tests/phpunit/Traits/DirsTrait.php b/tests/phpunit/Traits/DirsTrait.php
deleted file mode 100644
index 74318c7..0000000
--- a/tests/phpunit/Traits/DirsTrait.php
+++ /dev/null
@@ -1,50 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests\Traits;
-
-use AlexSkrypnyk\Customizer\Tests\Dirs;
-
-/**
- * Trait DirsTrait.
- *
- * Provides methods for working with Dirs class.
- */
-trait DirsTrait {
-
-  /**
-   * The fixture directories used in the test.
-   *
-   * @var \AlexSkrypnyk\Customizer\Tests\Dirs
-   */
-  protected $dirs;
-
-  /**
-   * Initialize the directories.
-   *
-   * @param callable|null $cb
-   *   Callback to run after initialization.
-   * @param string|null $root
-   *   The root directory.
-   */
-  protected function dirsInit(?callable $cb = NULL, string $root = NULL): void {
-    $this->dirs = new Dirs();
-    $this->dirs->initLocations($cb, $root);
-  }
-
-  /**
-   * Print directories' information.
-   */
-  protected function dirsInfo(): string {
-    return $this->dirs->printInfo();
-  }
-
-  /**
-   * Clean up directories.
-   */
-  protected function dirsClean(): void {
-    $this->dirs->deleteLocations();
-  }
-
-}
diff --git a/tests/phpunit/Traits/FileTrait.php b/tests/phpunit/Traits/FileTrait.php
deleted file mode 100644
index 6e03e66..0000000
--- a/tests/phpunit/Traits/FileTrait.php
+++ /dev/null
@@ -1,52 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace AlexSkrypnyk\Customizer\Tests\Traits;
-
-use Symfony\Component\Filesystem\Filesystem;
-
-/**
- * Trait to work with files.
- */
-trait FileTrait {
-
-  /**
-   * Find a directory where the file is located.
-   *
-   * @param string $file
-   *   The file to find.
-   * @param string|null $start
-   *   The directory to start the search from. If not provided, the current
-   *   file's directory will be used.
-   *
-   * @return string
-   *   The directory where the file is located.
-   */
-  public function fileFindDir(string $file, ?string $start = NULL): string {
-    if (empty($start)) {
-      $start = dirname(__FILE__);
-    }
-
-    $start = realpath($start);
-
-    if (empty($start)) {
-      throw new \RuntimeException('Failed to find the root directory of the repository.');
-    }
-
-    $fs = new Filesystem();
-
-    $current = $start;
-
-    while (!empty($current) && $current !== DIRECTORY_SEPARATOR) {
-      $path = $current . DIRECTORY_SEPARATOR . $file;
-      if ($fs->exists($path)) {
-        return $current;
-      }
-      $current = dirname($current);
-    }
-
-    throw new \RuntimeException('File not found: ' . $file);
-  }
-
-}
diff --git a/tests/phpunit/Unit/FilesTest.php b/tests/phpunit/Unit/FilesTest.php
index 1c2071c..bf6ee5b 100644
--- a/tests/phpunit/Unit/FilesTest.php
+++ b/tests/phpunit/Unit/FilesTest.php
@@ -5,78 +5,39 @@
 namespace AlexSkrypnyk\Customizer\Tests\Functional;
 
 use AlexSkrypnyk\Customizer\CustomizeCommand;
-use AlexSkrypnyk\Customizer\Tests\Traits\DirsTrait;
 use AlexSkrypnyk\Customizer\Tests\Traits\ReflectionTrait;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Group;
-use PHPUnit\Framework\TestCase;
-use PHPUnit\Framework\TestStatus\Failure;
 
 /**
  * Test for helpers used in operations on files.
  */
 #[CoversClass(CustomizeCommand::class)]
 #[Group('unit')]
-class FilesTest extends TestCase {
+class FilesTest extends CustomizerTestCase {
 
-  use DirsTrait;
   use ReflectionTrait;
 
   /**
    * {@inheritdoc}
    */
   protected function setUp(): void {
-    parent::setUp();
-
-    $this->dirsInit();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function tearDown(): void {
-    if (!$this->hasFailed()) {
-      $this->dirsClean();
-    }
-
-    parent::tearDown();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function onNotSuccessfulTest(\Throwable $t): never {
-    $this->dirsInfo();
-
-    // Rethrow the exception to allow the test to fail normally.
-    parent::onNotSuccessfulTest($t);
-  }
-
-  /**
-   * Check if the test has failed.
-   *
-   * @return bool
-   *   TRUE if the test has failed, FALSE otherwise.
-   */
-  public function hasFailed(): bool {
-    $status = $this->status();
-
-    return $status instanceof Failure;
+    $this->initLocations((string) getcwd());
   }
 
   #[DataProvider('dataProviderReplaceInPath')]
   public function testReplaceInPath(string $path, array $before, string $search, string $replace, bool $replaceLine, array $after): void {
-    $this->createFileTree($this->dirs->sut, $before);
+    $this->createFileTree(static::$sut, $before);
 
     CustomizeCommand::replaceInPath(
-      $this->dirs->sut . DIRECTORY_SEPARATOR . $path,
+      static::$sut . DIRECTORY_SEPARATOR . $path,
       $search,
       $replace,
       $replaceLine,
     );
 
-    $this->assertFileTree($this->dirs->sut, $after);
+    $this->assertFileTree(static::$sut, $after);
   }
 
   /**
@@ -264,17 +225,17 @@ public static function dataProviderReplaceInPath(): array {
 
   #[DataProvider('dataProviderReplaceInPathBetween')]
   public function testReplaceInPathBetween(string $path, array $before, string $search, string $replace, string $start, string $end, array $after): void {
-    $this->createFileTree($this->dirs->sut, $before);
+    $this->createFileTree(static::$sut, $before);
 
     CustomizeCommand::replaceInPathBetween(
-      $this->dirs->sut . DIRECTORY_SEPARATOR . $path,
+      static::$sut . DIRECTORY_SEPARATOR . $path,
       $search,
       $replace,
       $start,
       $end
     );
 
-    $this->assertFileTree($this->dirs->sut, $after);
+    $this->assertFileTree(static::$sut, $after);
   }
 
   /**
@@ -346,15 +307,15 @@ public static function dataProviderReplaceInPathBetween(): array {
 
   #[DataProvider('dataProviderUncommentLine')]
   public function testUncommentLine(string $path, array $before, string $search, string $marker, array $after): void {
-    $this->createFileTree($this->dirs->sut, $before);
+    $this->createFileTree(static::$sut, $before);
 
     CustomizeCommand::uncommentLine(
-      $this->dirs->sut . DIRECTORY_SEPARATOR . $path,
+      static::$sut . DIRECTORY_SEPARATOR . $path,
       $search,
       $marker
     );
 
-    $this->assertFileTree($this->dirs->sut, $after);
+    $this->assertFileTree(static::$sut, $after);
   }
 
   /**
@@ -404,7 +365,7 @@ public static function dataProviderUncommentLine(): array {
   #[DataProvider('dataProviderReadComposerJson')]
   public function testReadComposerJson(string $before, string $after, ?string $exception_message = NULL): void {
     if (!empty($before)) {
-      $this->createFileTree($this->dirs->sut, ['composer.json' => $before]);
+      $this->createFileTree(static::$sut, ['composer.json' => $before]);
     }
 
     if ($exception_message) {
@@ -412,10 +373,10 @@ public function testReadComposerJson(string $before, string $after, ?string $exc
       $this->expectExceptionMessage($exception_message);
     }
 
-    CustomizeCommand::readComposerJson($this->dirs->sut . '/composer.json');
+    CustomizeCommand::readComposerJson(static::$sut . '/composer.json');
 
     if (!$exception_message) {
-      $this->assertFileTree($this->dirs->sut, ['composer.json' => $after]);
+      $this->assertFileTree(static::$sut, ['composer.json' => $after]);
     }
   }
 
@@ -445,8 +406,8 @@ public static function dataProviderReadComposerJson(): array {
   }
 
   public function testWriteComposerJson(): void {
-    CustomizeCommand::writeComposerJson($this->dirs->sut . '/composer.json', [1, 2, 3]);
-    $this->assertFileTree($this->dirs->sut, [
+    CustomizeCommand::writeComposerJson(static::$sut . '/composer.json', [1, 2, 3]);
+    $this->assertFileTree(static::$sut, [
       'composer.json' => "[
     1,
     2,
diff --git a/tests/phpunit/Unit/SelfTest.php b/tests/phpunit/Unit/SelfTest.php
new file mode 100644
index 0000000..7277aa7
--- /dev/null
+++ b/tests/phpunit/Unit/SelfTest.php
@@ -0,0 +1,124 @@
+<?php
+
+declare(strict_types=1);
+
+namespace AlexSkrypnyk\Customizer\Tests\Unit;
+
+use AlexSkrypnyk\Customizer\CustomizeCommand;
+use AlexSkrypnyk\Customizer\Tests\Functional\CustomizerTestCase;
+use AlexSkrypnyk\Customizer\Tests\Traits\ReflectionTrait;
+use PHPUnit\Framework\AssertionFailedError;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Group;
+use Symfony\Component\Filesystem\Filesystem;
+
+/**
+ * Unit tests for the functional tests.
+ *
+ * These are "tests for tests" to make sure that the custom assertions
+ * provided by the CustomizerTestCase class work as expected.
+ *
+ * We inherit from CustomizerTestCase to test the custom assertions.
+ */
+#[CoversClass(CustomizeCommand::class)]
+#[Group('unit')]
+class SelfTest extends CustomizerTestCase {
+
+  use ReflectionTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    $this->fs = new Filesystem();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function tearDown(): void {
+    // Override the parent method as this is a unit test for a method of
+    // the parent test class.
+  }
+
+  #[DataProvider('dataProviderAssertDirectoriesEqual')]
+  public function testAssertDirectoriesEqual(array $diffs = []): void {
+    $base = getcwd() . DIRECTORY_SEPARATOR . static::FIXTURES_DIR . DIRECTORY_SEPARATOR . 'assert_fixture_files' . DIRECTORY_SEPARATOR . $this->dataName() . DIRECTORY_SEPARATOR . 'dir1';
+    $expected = getcwd() . DIRECTORY_SEPARATOR . static::FIXTURES_DIR . DIRECTORY_SEPARATOR . 'assert_fixture_files' . DIRECTORY_SEPARATOR . $this->dataName() . DIRECTORY_SEPARATOR . 'dir2';
+
+    try {
+      $this->assertDirectoriesEqual($base, $expected);
+    }
+    catch (AssertionFailedError $assertionFailedError) {
+      $this->assertExceptionMessage($assertionFailedError->getMessage(), $diffs);
+    }
+  }
+
+  /**
+   * Data provider for testAssertDirectoriesEqual().
+   *
+   * @return array
+   *   The data provider.
+   */
+  public static function dataProviderAssertDirectoriesEqual(): array {
+    return [
+      'files_equal' => [],
+      'files_not_equal' => [
+        [
+          'dir1' => [
+            'dir1_flat/d1f3-only-src.txt',
+          ],
+          'dir2' => [
+            'dir2_flat-present-dst/d2f1.txt',
+            'dir2_flat-present-dst/d2f2.txt',
+            'dir3_subdirs/dir31/f4-new-file-notignore-everywhere.txt',
+            'dir5_content_ignore/dir51/d51f2-new-file.txt',
+            'f4-new-file-notignore-everywhere.txt',
+          ],
+          'content' => [
+            'dir3_subdirs/dir32-unignored/d32f2.txt',
+          ],
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * Assert that the exception message contains the expected differences.
+   *
+   * @param string $message
+   *   The exception message.
+   * @param array $expected
+   *   The expected differences.
+   */
+  private function assertExceptionMessage(string $message, array $expected): void {
+    $actual = ['dir1' => [], 'dir2' => [], 'content' => []];
+
+    // Parse the exception message into sections.
+    $lines = explode("\n", trim($message));
+    $section = NULL;
+    foreach ($lines as $line) {
+      $line = trim($line);
+
+      if ($line === 'Files only in dir1:') {
+        $section = 'dir1';
+      }
+      elseif ($line === 'Files only in dir2:') {
+        $section = 'dir2';
+      }
+      elseif ($line === 'Files that differ in content:') {
+        $section = 'content';
+      }
+      elseif ($section) {
+        $actual[$section][] = $line;
+      }
+    }
+
+    // Compare the actual and expected sections.
+    foreach (['dir1', 'dir2', 'content'] as $section) {
+      $this->assertEquals($expected[$section] ?: [], $actual[$section] ?: [], sprintf("Files in section '%s' do not match expected.", $section));
+    }
+  }
+
+}