Fatal error: Uncaught Error: Class "Drupal\KernelTests\KernelTestBase" not found in /home/www/drupal8/test/core/modules/system/tests/src/Kernel/Block/SystemMenuBlockTest.php:27 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/system/tests/src/Kernel/Block/SystemMenuBlockTest.php on line 27