diff --git a/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php b/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php
index 197e3477ea..0dcef01615 100644
--- a/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php
+++ b/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php
@@ -4,6 +4,7 @@
 
 use Drupal\KernelTests\KernelTestBase;
 use Drupal\Setup\Commands\TestInstallationSetupApplication;
+use Drupal\Setup\SetupDrupalTestScript;
 use GuzzleHttp\Client;
 use GuzzleHttp\Psr7\Request;
 use Symfony\Component\Console\Tester\ApplicationTester;
@@ -39,7 +40,7 @@ public function testInstallScript() {
     $app_tester->run(
       [
         'command' => 'setup-drupal-test',
-        '--setup_file' => __DIR__ . '/../../../Setup/SetupDrupalTestScript.php',
+        '--setup_class' => SetupDrupalTestScript::class,
       ],
       [
         'interactive' => FALSE,
@@ -54,7 +55,7 @@ public function testInstallScript() {
     $http_client = new Client();
     $request = (new Request('GET', getenv('SIMPLETEST_BASE_URL') . '/test-page'))
       ->withHeader('User-Agent', trim($app_tester->getDisplay()));
-    
+
     $response = $http_client->send($request);
     // Ensure the test_page_test module got installed.
     $this->assertContains('Test page | Drupal', (string) $response->getBody());
diff --git a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
index 49fdafa1e2..8e81737a69 100644
--- a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
+++ b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
@@ -23,7 +23,7 @@ class TestInstallationSetupCommand extends Command {
    */
   protected function configure() {
     $this->setName('setup-drupal-test')
-      ->addOption('setup_file', NULL, InputOption::VALUE_OPTIONAL)
+      ->addOption('setup_class', NULL, InputOption::VALUE_OPTIONAL)
       ->addOption('db_url', NULL, InputOption::VALUE_OPTIONAL, 'URL for database or SIMPLETEST_DB', getenv('SIMPLETEST_DB'))
       ->addOption('base_url', NULL, InputOption::VALUE_OPTIONAL, 'Base URL for site under test or SIMPLETEST_BASE_URL', getenv('SIMPLETEST_BASE_URL'));
   }
@@ -41,7 +41,7 @@ protected function execute(InputInterface $input, OutputInterface $output) {
 
     // Manage site fixture.
     $test = new TestInstallationSetup();
-    $test->setup('testing', $input->getOption('setup_file'));
+    $test->setup('testing', $input->getOption('setup_class'));
 
     $output->writeln(drupal_generate_test_ua($test->getDatabasePrefix()));
   }
diff --git a/core/tests/Drupal/Setup/TestInstallationSetup.php b/core/tests/Drupal/Setup/TestInstallationSetup.php
index f2fd50f0b2..c57ad52bc4 100644
--- a/core/tests/Drupal/Setup/TestInstallationSetup.php
+++ b/core/tests/Drupal/Setup/TestInstallationSetup.php
@@ -46,18 +46,18 @@ class TestInstallationSetup {
    *
    * @param string $profile
    *   (optional) The installation profile to use.
-   * @param string $setup_file
-   *   (optional) Setup file. A PHP file to setup configuration used by the
+   * @param string $setup_class
+   *   (optional) Setup class. A PHP class to setup configuration used by the
    *   test.
    */
-  public function setup($profile = 'testing', $setup_file = NULL) {
+  public function setup($profile = 'testing', $setup_class = NULL) {
     $this->profile = $profile;
     $this->setupBaseUrl();
     $this->prepareEnvironment();
     $this->installDrupal();
 
-    if ($setup_file) {
-      $this->executeSetupFile($setup_file);
+    if ($setup_class) {
+      $this->executeSetupClass($setup_class);
     }
   }
 
@@ -87,18 +87,14 @@ protected function installDrupal() {
   /**
    * Uses the setup file to configure Drupal.
    *
-   * @param string $setup_file
-   *   The setup file.
+   * @param string $class
+   *   The setup class.
    */
-  protected function executeSetupFile($setup_file) {
-    $class = static::fileGetPhpClass($setup_file);
-
-    if (empty($class)) {
-      throw new \InvalidArgumentException(sprintf('You need to define a class implementing \Drupal\Setup\TestSetupInterface'));
+  protected function executeSetupClass($class) {
+    if (!class_exists($class)) {
+      throw new \InvalidArgumentException("There was a problem loading {$class}");
     }
 
-    require_once $setup_file;
-
     if (!is_subclass_of($class, TestSetupInterface::class)) {
       throw new \InvalidArgumentException(sprintf('You need to define a class implementing \Drupal\Setup\TestSetupInterface'));
     }
@@ -108,60 +104,6 @@ protected function executeSetupFile($setup_file) {
     $instance->setup();
   }
 
-  /**
-   * Gets the PHP classes contained in a php file.
-   *
-   * @param string $filepath
-   *   The file path.
-   *
-   * @return string|null
-   *   Returns a PHP class.
-   */
-  protected static function fileGetPhpClass($filepath) {
-    $php_code = file_get_contents($filepath);
-    return static::extractClassesFromPhp($php_code);
-  }
-
-  /**
-   * @param string $php_code
-   *   PHP code to parse.
-   *
-   * @return string
-   *   A PHP class.
-   */
-  protected static function extractClassesFromPhp($php_code) {
-    $tokens = token_get_all($php_code);
-
-    $class = $namespace = '';
-
-    for ($i = 0; $i < count($tokens); $i++) {
-      if ($tokens[$i][0] === T_NAMESPACE) {
-        for ($j = $i + 1; $j < count($tokens); $j++) {
-          if ($tokens[$j][0] === T_STRING) {
-            $namespace .= '\\' . $tokens[$j][1];
-          }
-          else {
-            if ($tokens[$j] === '{' || $tokens[$j] === ';') {
-              break;
-            }
-          }
-        }
-      }
-
-      if ($tokens[$i][0] === T_CLASS) {
-        for ($j = $i + 1; $j < count($tokens); $j++) {
-          if ($tokens[$j] === '{') {
-            $class = $tokens[$i + 2][1];
-          }
-        }
-      }
-    }
-
-    if ($namespace && $class) {
-      return $namespace . '\\' . $class;
-    }
-  }
-
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/Setup/TestSetupInterface.php b/core/tests/Drupal/Setup/TestSetupInterface.php
index 89bc2bda11..fe992161dc 100644
--- a/core/tests/Drupal/Setup/TestSetupInterface.php
+++ b/core/tests/Drupal/Setup/TestSetupInterface.php
@@ -9,7 +9,7 @@
 
   /**
    * Run code to setup the test.
-   * 
+   *
    * You have access to any API provided by any installed module. To install
    * modules use
    * @code
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index afce1d1e2e..17dc860dc1 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -149,7 +149,7 @@ function drupal_phpunit_populate_class_loader() {
 };
 
 // Do class loader population.
-$this_is_the_drupal_test_bootstrap_autoloader_so_do_not_be_confused = drupal_phpunit_populate_class_loader();
+drupal_phpunit_populate_class_loader();
 
 // Set sane locale settings, to ensure consistent string, dates, times and
 // numbers handling.
@@ -184,5 +184,3 @@ class_alias('\PHPUnit\Framework\TestCase', '\PHPUnit_Framework_TestCase');
   class_alias('\PHPUnit\Util\Test', '\PHPUnit_Util_Test');
   class_alias('\PHPUnit\Util\XML', '\PHPUnit_Util_XML');
 }
-
-return $this_is_the_drupal_test_bootstrap_autoloader_so_do_not_be_confused;