Fatal error: Uncaught Error: Class "Drupal\Core\Plugin\DefaultPluginManager" not found in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php:13
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php on line 13