Fatal error: Uncaught Error: Class "Drupal\Tests\Core\Plugin\Discovery\TestDerivativeDiscovery" not found in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/Discovery/TestContainerDerivativeDiscovery.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Plugin/Discovery/TestContainerDerivativeDiscovery.php on line 12