Fatal error: Uncaught Error: Class "PHPUnit\Framework\TestSuite" not found in /home/www/drupal8/test/core/tests/TestSuites/TestSuiteBase.php:11
Stack trace:
#0 /home/www/drupal8/test/core/tests/Drupal/Tests/Core/Test/TestSuiteBaseTest.php(11): require_once()
#1 {main}
thrown in /home/www/drupal8/test/core/tests/TestSuites/TestSuiteBase.php on line 11