Improve pip package manager tests

tests/fixtures/pip_basic/requirements.txt

@@ -1,2 +1,2 @@
 # This package has been picked since it has no dependencies and is small/fast to install.
-typing-extensions==4.7.1
+typing-extensions==4.12.2

tests/fixtures/pip_editable_git_compiled/requirements.txt

@@ -8,4 +8,4 @@
 # The URL to the package is specified via env var, to test that user-provided env vars
 # are propagated to pip for use by its env var interpolation feature.
 
--e git+${WHEEL_PACKAGE_URL}@0.40.0#egg=extension.dist&subdirectory=tests/testdata/extension.dist
+-e git+${WHEEL_PACKAGE_URL}@0.44.0#egg=extension.dist&subdirectory=tests/testdata/extension.dist

tests/fixtures/testing_buildpack/bin/build

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+# Check that:
+# - The correct env vars are set for later buildpacks.
+# - Python's sys.path is correct.
+# - The correct version of pip was installed.
+# - Both the package manager and Python can find the typing-extensions package.
+# - The system site-packages directory is protected against running 'pip install'
+#   without having passed '--user'.
+# - The typing-extensions package was installed into a separate dependencies layer.
+
+set -euo pipefail
+
+echo
+echo "## Testing buildpack ##"
+
+printenv | sort | grep -vE '^(_|CNB_.+|HOME|HOSTNAME|OLDPWD|PWD|SHLVL)='
+echo
+python -c 'import pprint, sys; pprint.pp(sys.path)'
+echo
+pip --version
+pip list
+pip install --dry-run typing-extensions
+python -c 'import typing_extensions; print(typing_extensions)'

tests/fixtures/testing_buildpack/bin/detect

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+exit 0

tests/fixtures/testing_buildpack/buildpack.toml

@@ -0,0 +1,6 @@
+api = "0.11"
+
+[buildpack]
+id = "testing-buildpack"
+version = "0.0.0"
+clear-env = true

tests/mod.rs

@@ -3,16 +3,16 @@
 //! These tests are not run via automatic integration test discovery, but instead are
 //! imported in main.rs so that they have access to private APIs (see comment in main.rs).
 
-use libcnb_test::BuildConfig;
-use std::env;
-use std::path::Path;
-
 mod detect_test;
 mod django_test;
 mod package_manager_test;
 mod pip_test;
 mod python_version_test;
 
+use libcnb_test::BuildConfig;
+use std::env;
+use std::path::Path;
+
 const LATEST_PYTHON_3_7: &str = "3.7.17";
 const LATEST_PYTHON_3_8: &str = "3.8.19";
 const LATEST_PYTHON_3_9: &str = "3.9.19";