Fatal error: Uncaught Error: Class "Drupal\KernelTests\Core\Cache\GenericCacheBackendUnitTestBase" not found in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Cache/PhpBackendTest.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Cache/PhpBackendTest.php on line 12