Fatal error: Uncaught Error: Class "Drupal\Core\Plugin\DefaultPluginManager" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Validation/ConstraintManager.php:29
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Validation/ConstraintManager.php on line 29