Fatal error: Uncaught Error: Class "Drupal\KernelTests\KernelTestBase" not found in /home/www/drupal8/test/core/modules/block/tests/src/Kernel/BlockRebuildTest.php:15
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/block/tests/src/Kernel/BlockRebuildTest.php on line 15