Fatal error: Uncaught Error: Class "Drupal\simpletest\WebTestBase" not found in /home/www/drupal8/test/core/modules/system/src/Tests/Cache/CacheTestBase.php:13
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/system/src/Tests/Cache/CacheTestBase.php on line 13