Fatal error: Uncaught Error: Class "Drupal\Component\Plugin\PluginBase" not found in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/Fixtures/TestConfigurablePlugin.php:8 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/Fixtures/TestConfigurablePlugin.php on line 8