diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d008d38fad3..01711637fd0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -245,17 +245,11 @@ jobs:
         with:
           java-version: 1.8
 
-      - name: Build unscoped PHAR for testing
-        run: ant unscoped-phar-snapshot
-
       - name: Run regular tests with unscoped PHAR
-        run: ./build/artifacts/phpunit-snapshot.phar
-
-      - name: Build scoped PHAR for testing
-        run: ant phar-snapshot
+        run: ant run-regular-tests-with-unscoped-phar
 
       - name: Run PHAR-specific tests with scoped PHAR
-        run: ./build/artifacts/phpunit-snapshot.phar --configuration tests/phar/phpunit.xml
+        run: ant run-phar-specific-tests-with-scoped-phar
 
       - uses: actions/upload-artifact@v2
         if: ${{ matrix.php-version == 8.0 }}
diff --git a/build.xml b/build.xml
index b5cf5a973e4..ff2a152e95b 100644
--- a/build.xml
+++ b/build.xml
@@ -119,7 +119,7 @@
         </antcall>
     </target>
 
-    <target name="unscoped-phar" depends="-phar-prepare,-phar-determine-version" description="Create PHAR archive of PHPUnit and all its dependencies">
+    <target name="unscoped-phar" depends="-phar-prepare,-phar-determine-version" description="Create unscoped PHAR archive of PHPUnit and all its dependencies">
         <antcall target="-phar-build">
             <param name="type" value="release"/>
             <param name="scope" value="false"/>
@@ -133,7 +133,7 @@
         </antcall>
     </target>
 
-    <target name="unscoped-phar-snapshot" depends="-phar-prepare" description="Create PHAR archive of PHPUnit and all its dependencies (snapshot)">
+    <target name="unscoped-phar-snapshot" depends="-phar-prepare" description="Create unscoped PHAR archive of PHPUnit and all its dependencies (snapshot)">
         <antcall target="-phar-build">
             <param name="type" value="snapshot"/>
             <param name="scope" value="false"/>
@@ -432,6 +432,36 @@
         <exec executable="${basedir}/build/scripts/version.php" outputproperty="version" failonerror="true" />
     </target>
 
+    <target name="run-regular-tests-with-unscoped-phar" depends="clean,unscoped-phar-snapshot" description="Build unscoped PHAR snapshot and run the regular test suite with it">
+        <exec executable="${basedir}/tools/phpab" taskname="phpab" failonerror="true">
+            <arg value="--output" />
+            <arg path="${basedir}/tests/autoload.php" />
+            <arg path="${basedir}/tests/_files" />
+            <arg path="${basedir}/tests/end-to-end/execution-order/_files" />
+            <arg path="${basedir}/tests/unit" />
+        </exec>
+
+        <delete dir="${basedir}/vendor"/>
+        <delete file="${basedir}/composer.lock"/>
+
+        <exec executable="${basedir}/build/artifacts/phpunit-snapshot.phar" taskname="phpunit" failonerror="true">
+            <arg value="--testsuite" />
+            <arg value="unit" />
+        </exec>
+
+        <delete file="${basedir}/tests/autoload.php"/>
+    </target>
+
+    <target name="run-phar-specific-tests-with-scoped-phar" depends="clean,phar-snapshot" description="Build scoped PHAR snapshot and run the PHAR-specific tests with it">
+        <delete dir="${basedir}/vendor"/>
+        <delete file="${basedir}/composer.lock"/>
+
+        <exec executable="${basedir}/build/artifacts/phpunit-snapshot.phar" taskname="phpunit" failonerror="true">
+            <arg value="--configuration" />
+            <arg value="tests/phar/phpunit.xml" />
+        </exec>
+    </target>
+
     <target name="generate-project-documentation" depends="-phploc,-checkstyle,-phpunit">
         <exec executable="${basedir}/tools/phpdox" dir="${basedir}/build/config" taskname="phpdox"/>
     </target>
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index ea96b20002b..2878b70b560 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -9,8 +9,35 @@
  */
 const TEST_FILES_PATH = __DIR__ . DIRECTORY_SEPARATOR . '_files' . DIRECTORY_SEPARATOR;
 
-if (!defined('PHPUNIT_COMPOSER_INSTALL')) {
-    define('PHPUNIT_COMPOSER_INSTALL', dirname(__DIR__) . '/vendor/autoload.php');
+if (file_exists(__DIR__ . '/../vendor/autoload.php')) {
+    if (!defined('PHPUNIT_COMPOSER_INSTALL')) {
+        define('PHPUNIT_COMPOSER_INSTALL', dirname(__DIR__) . '/vendor/autoload.php');
+    }
+
+    require_once __DIR__ . '/../vendor/autoload.php';
+
+    return;
+}
+
+if (file_exists(__DIR__ . '/autoload.php')) {
+    if (!defined('__PHPUNIT_PHAR__')) {
+        define('__PHPUNIT_PHAR__', realpath($_SERVER['_']));
+    }
+
+    require_once __DIR__ . '/autoload.php';
+
+    $jsonFile = dirname(__DIR__) . '/composer.json';
+    $base     = dirname($jsonFile);
+
+    foreach (json_decode(file_get_contents($jsonFile), true)['autoload-dev']['files'] as $file) {
+        require_once $base . DIRECTORY_SEPARATOR . $file;
+    }
+
+    unset($jsonFile, $base, $file);
+
+    return;
 }
 
-require_once PHPUNIT_COMPOSER_INSTALL;
+print 'No test fixture autoloader was registered, exiting.' . \PHP_EOL;
+
+exit(1);