Fatal error: Uncaught Error: Class "Drupal\Tests\aggregator\Functional\AggregatorTestBase" not found in /home/www/drupal8/test/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php on line 12