Fatal error: Uncaught Error: Class "Drupal\Tests\BrowserTestBase" not found in /home/www/drupal8/test/core/modules/simpletest/tests/fixtures/simpletest_phpunit_browsertest.php:14 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/simpletest/tests/fixtures/simpletest_phpunit_browsertest.php on line 14