diff --git a/test/EndToEnd/Version10/DefaultConfiguration/SleeperTest.php b/test/EndToEnd/Version10/DefaultConfiguration/SleeperTest.php
index e094eb80..4bc259b1 100644
--- a/test/EndToEnd/Version10/DefaultConfiguration/SleeperTest.php
+++ b/test/EndToEnd/Version10/DefaultConfiguration/SleeperTest.php
@@ -359,4 +359,32 @@ public static function provideMillisecondsGreaterThanDefaultMaximumDuration(): i
             ];
         }
     }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsShorterThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 50;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 750;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
 }
diff --git a/test/EndToEnd/Version10/DefaultConfiguration/test.phpt b/test/EndToEnd/Version10/DefaultConfiguration/test.phpt
index 4172fa11..0a24f6a3 100644
--- a/test/EndToEnd/Version10/DefaultConfiguration/test.phpt
+++ b/test/EndToEnd/Version10/DefaultConfiguration/test.phpt
@@ -9,7 +9,9 @@ use PHPUnit\TextUI;
 
 $_SERVER['argv'][] = '--configuration=test/EndToEnd/Version10/DefaultConfiguration/phpunit.xml';
 
-require_once __DIR__ . '/../../../../vendor/autoload.php';
+define('PHPUNIT_COMPOSER_INSTALL', __DIR__ . '/../../../../vendor/autoload.php');
+
+require_once PHPUNIT_COMPOSER_INSTALL;
 
 $application = new TextUI\Application();
 
@@ -21,23 +23,23 @@ Runtime: %s
 Configuration: %Stest/EndToEnd/Version10/DefaultConfiguration/phpunit.xml
 Random %seed:   %s
 
-.......................                                           23 / 23 (100%)
+.........................                                         25 / 25 (100%)
 
-Detected 13 tests that took longer than expected.
+Detected 14 tests that took longer than expected.
 
  1. 1.30%s (1.150) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAttributeWithValidMaximumDurationAndSlowThresholdAnnotation
  2. 1.25%s (1.100) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAttribute
  3. 1.20%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidSlowThresholdAndMaximumDurationAnnotation
  4. 1.15%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAndSlowThresholdAnnotation
  5. 1.10%s (0.900) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanSlowThresholdFromAnnotationWithValidSlowThresholdAnnotation
- 6. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
- 7. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
- 8. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
- 9. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
-10. 0.85%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDuration
+ 6. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration
+ 7. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
+ 8. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
+ 9. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
+10. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version10\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
 
-There are 3 additional slow tests that are not listed here.
+There are 4 additional slow tests that are not listed here.
 
 Time: %s, Memory: %s
 
-OK (23 tests, 23 assertions)
+OK (25 tests, 25 assertions)
diff --git a/test/EndToEnd/Version8/DefaultConfiguration/SleeperTest.php b/test/EndToEnd/Version8/DefaultConfiguration/SleeperTest.php
index db88730e..3ac4bc78 100644
--- a/test/EndToEnd/Version8/DefaultConfiguration/SleeperTest.php
+++ b/test/EndToEnd/Version8/DefaultConfiguration/SleeperTest.php
@@ -304,4 +304,32 @@ public static function provideMillisecondsGreaterThanDefaultMaximumDuration(): i
             ];
         }
     }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsShorterThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 50;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 750;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
 }
diff --git a/test/EndToEnd/Version8/DefaultConfiguration/test.phpt b/test/EndToEnd/Version8/DefaultConfiguration/test.phpt
index 64cf95d0..38e56850 100644
--- a/test/EndToEnd/Version8/DefaultConfiguration/test.phpt
+++ b/test/EndToEnd/Version8/DefaultConfiguration/test.phpt
@@ -9,7 +9,9 @@ use PHPUnit\TextUI;
 
 $_SERVER['argv'][] = '--configuration=test/EndToEnd/Version8/DefaultConfiguration/phpunit.xml';
 
-require_once __DIR__ . '/../../../../vendor/autoload.php';
+define('PHPUNIT_COMPOSER_INSTALL', __DIR__ . '/../../../../vendor/autoload.php');
+
+require_once PHPUNIT_COMPOSER_INSTALL;
 
 PHPUnit\TextUI\Command::main();
 --EXPECTF--
@@ -19,23 +21,23 @@ Runtime: %s
 Configuration: %Stest/EndToEnd/Version8/DefaultConfiguration/phpunit.xml
 Random %seed:   %s
 
-...................                                               19 / 19 (100%)
+.....................                                             21 / 21 (100%)
 
-Detected 11 tests that took longer than expected.
+Detected 12 tests that took longer than expected.
 
  1. 1.20%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidSlowThresholdAndMaximumDurationAnnotation
  2. 1.15%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAndSlowThresholdAnnotation
  3. 1.10%s (0.900) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanSlowThresholdFromAnnotationWithValidSlowThresholdAnnotation
- 4. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
- 5. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
- 6. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
- 7. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
- 8. 0.85%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDuration
- 9. 0.70%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #2 (600)
-10. 0.65%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #1 (550)
+ 4. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration
+ 5. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
+ 6. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
+ 7. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
+ 8. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
+ 9. 0.85%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDuration
+10. 0.70%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version8\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #2 (600)
 
-There is 1 additional slow test that is not listed here.
+There are 2 additional slow tests that are not listed here.
 
 Time: %s, Memory: %s
 
-OK (19 tests, 19 assertions)
+OK (21 tests, 21 assertions)
diff --git a/test/EndToEnd/Version9/DefaultConfiguration/SleeperTest.php b/test/EndToEnd/Version9/DefaultConfiguration/SleeperTest.php
index 1dcbc408..857837b8 100644
--- a/test/EndToEnd/Version9/DefaultConfiguration/SleeperTest.php
+++ b/test/EndToEnd/Version9/DefaultConfiguration/SleeperTest.php
@@ -304,4 +304,32 @@ public static function provideMillisecondsGreaterThanDefaultMaximumDuration(): i
             ];
         }
     }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsShorterThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 50;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration(): void
+    {
+        $milliseconds = 750;
+
+        $sleeper = Test\Fixture\Sleeper::fromMilliseconds($milliseconds);
+
+        $sleeper->sleep();
+
+        self::assertSame($milliseconds, $sleeper->milliseconds());
+    }
 }
diff --git a/test/EndToEnd/Version9/DefaultConfiguration/test.phpt b/test/EndToEnd/Version9/DefaultConfiguration/test.phpt
index 5f35cb6d..868cb8c7 100644
--- a/test/EndToEnd/Version9/DefaultConfiguration/test.phpt
+++ b/test/EndToEnd/Version9/DefaultConfiguration/test.phpt
@@ -9,7 +9,9 @@ use PHPUnit\TextUI;
 
 $_SERVER['argv'][] = '--configuration=test/EndToEnd/Version9/DefaultConfiguration/phpunit.xml';
 
-require_once __DIR__ . '/../../../../vendor/autoload.php';
+define('PHPUNIT_COMPOSER_INSTALL', __DIR__ . '/../../../../vendor/autoload.php');
+
+require_once PHPUNIT_COMPOSER_INSTALL;
 
 PHPUnit\TextUI\Command::main();
 --EXPECTF--
@@ -19,23 +21,23 @@ Runtime: %s
 Configuration: %Stest/EndToEnd/Version9/DefaultConfiguration/phpunit.xml
 Random %seed:   %s
 
-...................                                               19 / 19 (100%)
+.....................                                             21 / 21 (100%)
 
-Detected 11 tests that took longer than expected.
+Detected 12 tests that took longer than expected.
 
  1. 1.20%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidSlowThresholdAndMaximumDurationAnnotation
  2. 1.15%s (1.000) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAndSlowThresholdAnnotation
  3. 1.10%s (0.900) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanSlowThresholdFromAnnotationWithValidSlowThresholdAnnotation
- 4. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
- 5. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
- 6. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
- 7. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
- 8. 0.85%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDuration
- 9. 0.70%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #2 (600)
-10. 0.65%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #1 (550)
+ 4. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testRunInSeparateProcessSleeperSleepsLongerThanDefaultMaximumDuration
+ 5. 1.05%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidSlowThresholdAnnotation
+ 6. 1.00%s (0.800) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanMaximumDurationFromAnnotationWithValidMaximumDurationAnnotation
+ 7. 0.95%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithInvalidMaximumDurationAnnotation
+ 8. 0.90%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithUselessDocBlock
+ 9. 0.85%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDuration
+10. 0.70%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Version9\DefaultConfiguration\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider with data set #2 (600)
 
-There is 1 additional slow test that is not listed here.
+There are 2 additional slow tests that are not listed here.
 
 Time: %s, Memory: %s
 
-OK (19 tests, 19 assertions)
+OK (21 tests, 21 assertions)