Fatal error: Uncaught Error: Class "Drupal\Tests\Core\Render\RendererTestBase" not found in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php:22 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php on line 22