Fatal error: Uncaught Error: Class "Drupal\FunctionalTests\Installer\InstallerTestBase" not found in /home/www/drupal8/test/core/tests/Drupal/FunctionalTests/Installer/ConfigAfterInstallerTestBase.php:13 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/FunctionalTests/Installer/ConfigAfterInstallerTestBase.php on line 13