Fatal error: Uncaught Error: Class "Drupal\Tests\update\Functional\UpdateTestBase" not found in /home/www/drupal8/test/core/modules/update/tests/src/Functional/UpdateContribTest.php:14
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/update/tests/src/Functional/UpdateContribTest.php on line 14