Fatal error: Uncaught Error: Class "Drupal\Tests\system\Functional\Database\DatabaseTestBase" not found in /home/www/drupal8/test/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php on line 12