[TASK] Reset GeneraulUtility::$container in UnitTestCase::tearDown()

It could be possible that unit tests sets dependency injection
container calling `GeneralUtility::setContainer()` to provide
service instances or mocked service instances specific bound
to that test, keeping a dirty state for following unit tests.

Executing unit tests in other orders, only as a subset or for
example randomized can reveal these pullation and eventualy
wrong expectation for other tests. [1]

This change adds a automatic cleanup to the tearDown for
unit tests ensuring a clean state, because there isn't a
easy way to reset that within tests without using native
php reflection API. So do it in a general place.

It may be possible to let the specific test setting such
a container intance to fail with the recommendation to
refactor the test into a functional test, but is left out
for now.

[1] https://review.typo3.org/c/Packages/TYPO3.CMS/+/88839

Releases: main, 8, 7

Author: sbuerk

Classes/Core/Unit/UnitTestCase.php

@@ -136,6 +136,18 @@ protected function tearDown(): void
             }
         }
 
+        // Unit tests may set GeneralUtility::setContainer() with a container instance containing mocked services,
+        // returning test specific results. Following tests may not expect that specific outcome and thus fail when
+        // executed in another order (for example using randomized unit tests). Not having a suitable API to reset
+        // container instance to null we are using reflection API to reset that property in each teardown to ensure
+        // clean state for following tests.
+        $containerPropertyReflection = new \ReflectionProperty(GeneralUtility::class, 'container');
+        if ($containerPropertyReflection->getValue(null) !== null) {
+            // Reset container instances set with `GeneralUtility::setContainer()`.
+            $containerPropertyReflection->setValue(null, null);
+            // @todo Should we fail the test recommending to transform the test to an functional test ?
+        }
+
         // Delete registered test files and directories
         foreach ($this->testFilesToDelete as $absoluteFileName) {
             $absoluteFileName = GeneralUtility::fixWindowsFilePath(PathUtility::getCanonicalPath($absoluteFileName));