Fatal error: Uncaught Error: Class "Drupal\Tests\BrowserTestBase" not found in /home/www/drupal8/test/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php:15 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php on line 15