Fatal error: Uncaught Error: Class "Drupal\KernelTests\ConfigFormTestBase" not found in /home/www/drupal8/test/core/modules/user/tests/src/Kernel/UserAdminSettingsFormTest.php:13 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/user/tests/src/Kernel/UserAdminSettingsFormTest.php on line 13