Fatal error: Uncaught Error: Class "Drupal\Tests\BrowserTestBase" not found in /home/qcsvlel/www/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php:18 Stack trace: #0 {main} thrown in /home/qcsvlel/www/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php on line 18