Fatal error: Uncaught Error: Class "Drupal\KernelTests\Core\Database\DatabaseTestBase" not found in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Database/SelectSubqueryTest.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/KernelTests/Core/Database/SelectSubqueryTest.php on line 10