Fatal error: Uncaught Error: Interface "Drupal\Core\Theme\ThemeManagerInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Theme/ThemeManager.php:15 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Theme/ThemeManager.php on line 15