Fatal error: Uncaught Error: Class 'Drupal\Tests\UnitTestCase' not found in /var/www/html/tmp/contrib/flag/tests/src/Unit/Plugin/Action/FlagActionTest.php:21 Stack trace: #0 {main} thrown in /var/www/html/tmp/contrib/flag/tests/src/Unit/Plugin/Action/FlagActionTest.php on line 21