Fatal error: Uncaught Error: Class "Drupal\KernelTests\KernelTestBase" not found in /home/www/drupal8/test/core/modules/system/tests/src/Functional/Entity/EntityReferenceSelection/EntityReferenceSelectionAccessTest.php:26 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/system/tests/src/Functional/Entity/EntityReferenceSelection/EntityReferenceSelectionAccessTest.php on line 26