Fatal error: Uncaught Error: Class "Drupal\Component\Plugin\PluginManagerBase" not found in /home/www/drupal8/test/core/tests/Drupal/Tests/Component/Plugin/StubFallbackPluginManager.php:18 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/Tests/Component/Plugin/StubFallbackPluginManager.php on line 18