Fatal error: Uncaught Error: Interface "Drupal\Core\Cache\CacheBackendInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Cache/PhpBackend.php:22 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Cache/PhpBackend.php on line 22