diff --git a/core/modules/simpletest/tests/fixtures/simpletest_phpunit_run_command_test.php b/core/modules/simpletest/tests/fixtures/simpletest_phpunit_run_command_test.php
index f9874c0..839f008 100644
--- a/core/modules/simpletest/tests/fixtures/simpletest_phpunit_run_command_test.php
+++ b/core/modules/simpletest/tests/fixtures/simpletest_phpunit_run_command_test.php
@@ -4,10 +4,18 @@
 
 use Drupal\Tests\UnitTestCase;
 
+/**
+ * This test crashes PHP.
+ *
+ * To avoid accidentally running, it is not in a normal PSR-4 directory, the
+ * file name does not adhere to PSR-4 and an environment variable also needs to
+ * be set for the crash to happen.
+ */
 class SimpletestPhpunitRunCommandTestWillDie extends UnitTestCase {
 
-  function testWillDie() {
+  public function testWillDie() {
     if (getenv('SimpletestPhpunitRunCommandTestWillDie') === 'fail') {
+      // This causes a segmentation fault.
       preg_match('/(.(?!b))*/', str_repeat("a", 10000));
     }
   }
diff --git a/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php b/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
index a371891..f49fe5f 100644
--- a/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
+++ b/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
@@ -11,7 +11,12 @@
 use Drupal\Tests\UnitTestCase;
 
 /**
+ * Tests simpletest_run_phpunit_tests() handles PHPunit fatals correctly.
+ *
  * @group simpletest
+ *
+ * @runTestsInSeparateProcesses
+ * @preserveGlobalState disabled
  */
 class SimpletestPhpunitRunCommandTest extends UnitTestCase {