Update to Drupal 8.0.2. For more information, see https://www.drupal.org/drupal-8.0.2-release-notes

core/modules/simpletest/tests/fixtures/simpletest_phpunit_run_command_test.php

@@ -17,6 +17,7 @@ class SimpletestPhpunitRunCommandTestWillDie extends UnitTestCase {
     if (getenv('SimpletestPhpunitRunCommandTestWillDie') === 'fail') {
       exit(2);
     }
+    $this->assertTrue(TRUE, 'Assertion to ensure test pass');
   }
 }
 

core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php

@@ -13,9 +13,6 @@ use Drupal\simpletest\BrowserTestBase;
  * Tests BrowserTestBase functionality.
  *
  * @group simpletest
- *
- * @runTestsInSeparateProcesses
- * @preserveGlobalState disabled
  */
 class BrowserTestBaseTest extends BrowserTestBase {