diff --git a/core/lib/Drupal/Core/Test/TestSetupTrait.php b/core/lib/Drupal/Core/Test/TestSetupTrait.php
index 44409078db..8bef66c3dc 100644
--- a/core/lib/Drupal/Core/Test/TestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/TestSetupTrait.php
@@ -159,6 +159,8 @@ protected function changeDatabasePrefix() {
     $db_url = getenv('SIMPLETEST_DB');
     if (!empty($db_url)) {
       $database = Database::convertDbUrlToConnectionInfo($db_url, isset($this->root) ? $this->root : DRUPAL_ROOT);
+      // Ensure that the connection is added.
+      Database::removeConnection('default');
       Database::addConnectionInfo('default', 'default', $database);
     }
 
diff --git a/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php b/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php
deleted file mode 100644
index fb45b50527..0000000000
--- a/core/tests/Drupal/KernelTests/Setup/Commands/SetupDrupalTestScriptTest.php
+++ /dev/null
@@ -1,211 +0,0 @@
-<?php
-
-namespace Drupal\KernelTests\Setup\Commands;
-
-use Drupal\Core\Database\Database;
-use Drupal\Core\Test\TestDatabase;
-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;
-
-/**
- * Tests setup-drupal-test.php.
- *
- * @group Setup
- *
- * @see \Drupal\Setup\Commands\TestInstallationSetupApplication
- * @see \Drupal\Setup\Commands\TestInstallationSetupCommand
- * @see \Drupal\Setup\Commands\TestTeardownCommand
- */
-class SetupDrupalTestScriptTest extends KernelTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    // Disable the usual kernel test setup process, as we want to run a custom
-    // command to install Drupal.
-    $this->root = static::getDrupalRoot();
-  }
-
-  /**
-   * @coversNothing
-   */
-  public function testInstallWithNonExistingClass() {
-    $autoloader = $this->root . '/autoload.php';
-    $app = new TestInstallationSetupApplication(require $autoloader);
-    $app->setAutoExit(FALSE);
-
-    $app_tester = new ApplicationTester($app);
-    $app_tester->run(
-      [
-        'command' => 'setup-drupal-test',
-        '--setup_class' => 'this-class-does-not-exist',
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-
-    $this->assertContains('There was a problem loading this-class-does-not-exist', $app_tester->getDisplay());
-  }
-
-  /**
-   * @coversNothing
-   */
-  public function testInstallWithNonSetupClass() {
-    $autoloader = $this->root . '/autoload.php';
-    $app = new TestInstallationSetupApplication(require $autoloader);
-    $app->setAutoExit(FALSE);
-
-    $app_tester = new ApplicationTester($app);
-    $app_tester->run(
-      [
-        'command' => 'setup-drupal-test',
-        '--setup_class' => static::class,
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-
-    $this->assertContains('You need to define a class implementing \Drupal\Setup\TestSetupInterface ', $app_tester->getDisplay());
-  }
-
-  /**
-   * @coversNothing
-   */
-  public function testInstallScript() {
-    $autoloader = $this->root . '/autoload.php';
-    $app = new TestInstallationSetupApplication(require $autoloader);
-    $app->setAutoExit(FALSE);
-
-    $app_tester = new ApplicationTester($app);
-    $app_tester->run(
-      [
-        'command' => 'setup-drupal-test',
-        '--setup_class' => SetupDrupalTestScript::class,
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-
-    $this->assertNotRegExp('/PHPUnit_Framework_Error_Warning/', $app_tester->getDisplay());
-    $this->assertNotRegExp('/AlreadyInstalledException/', $app_tester->getDisplay());
-
-    $result = json_decode($app_tester->getDisplay(), TRUE);
-    $db_prefix = $result['db_prefix'];
-    $this->assertNotEmpty($db_prefix);
-    $this->assertStringStartsWith('simpletest' . substr($db_prefix, 4) . ':', $result['user_agent']);
-
-    $this->assertEquals(0, $app_tester->getStatusCode());
-
-    $http_client = new Client();
-    $request = (new Request('GET', getenv('SIMPLETEST_BASE_URL') . '/test-page'))
-      ->withHeader('User-Agent', trim($result['user_agent']));
-
-    $response = $http_client->send($request);
-    // Ensure the test_page_test module got installed.
-    $this->assertContains('Test page | Drupal', (string) $response->getBody());
-
-    // Ensure that there are files and database tables for teardown to clean up.
-    $this->addTestDatabase($db_prefix);
-    $this->assertGreaterThan(0, count(Database::getConnection(__CLASS__)->schema()->findTables('%')));
-    $test_database = new TestDatabase($db_prefix);
-    $test_file = $test_database->getTestSitePath() . DIRECTORY_SEPARATOR . '.htkey';
-    $this->assertFileExists($test_file);
-
-    // Now test the tear down process as well.
-    $status = $app_tester->run(
-      [
-        'command' => 'teardown-drupal-test',
-        'db_prefix' => "$db_prefix",
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-    $this->assertSame(0, $status);
-
-    // Ensure that all the tables and files for this DB prefix are gone.
-    $this->assertCount(0, Database::getConnection(__CLASS__)->schema()->findTables('%'));
-    $this->assertFileNotExists($test_file);
-  }
-
-  /**
-   * @coversNothing
-   */
-  public function testInstallInDifferentLanguage() {
-    $autoloader = $this->root . '/autoload.php';
-    $app = new TestInstallationSetupApplication(require $autoloader);
-    $app->setAutoExit(FALSE);
-
-    $app_tester = new ApplicationTester($app);
-    $app_tester->run(
-      [
-        'command' => 'setup-drupal-test',
-        '--langcode' => 'fr',
-        '--setup_class' => SetupDrupalTestScript::class,
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-
-    $this->assertNotRegExp('/PHPUnit_Framework_Error_Warning/', $app_tester->getDisplay());
-    $this->assertNotRegExp('/AlreadyInstalledException/', $app_tester->getDisplay());
-    $this->assertEquals(0, $app_tester->getStatusCode());
-
-    $result = json_decode($app_tester->getDisplay(), TRUE);
-    $db_prefix = $result['db_prefix'];
-    $http_client = new Client();
-    $request = (new Request('GET', getenv('SIMPLETEST_BASE_URL') . '/test-page'))
-      ->withHeader('User-Agent', trim($result['user_agent']));
-
-    $response = $http_client->send($request);
-    // Ensure the test_page_test module got installed.
-    $this->assertContains('Test page | Drupal', (string) $response->getBody());
-    $this->assertContains('lang="fr"', (string) $response->getBody());
-
-    // Now test the tear down process as well.
-    $app_tester->run(
-      [
-        'command' => 'teardown-drupal-test',
-        'db_prefix' => $db_prefix,
-      ],
-      [
-        'interactive' => FALSE,
-      ]
-    );
-
-    // Ensure that all the tables for this DB prefix are gone.
-    $this->addTestDatabase($db_prefix);
-    $this->assertCount(0, Database::getConnection(__CLASS__)->schema()->findTables('%'));
-  }
-
-  /**
-   * Adds the installed test site to the database connection info.
-   *
-   * The target for the added connection is the class name of the test.
-   *
-   * @param $db_prefix
-   *   The prefix of the installed test site.
-   */
-  protected function addTestDatabase($db_prefix) {
-    // Use the original database connection info.
-    $connection_info = Database::getConnectionInfo('simpletest_original_default');
-    if (!empty($connection_info)) {
-      foreach ($connection_info as $target => $value) {
-        $connection_info[$target]['prefix'] = [
-          'default' => $value['prefix']['default'] . $db_prefix,
-        ];
-      }
-    }
-    Database::addConnectionInfo('default', __CLASS__, $connection_info['default']);
-  }
-
-}
diff --git a/core/tests/Drupal/Setup/Commands/TestInstallationSetupApplication.php b/core/tests/Drupal/Setup/Commands/TestInstallationSetupApplication.php
index 15a5ab1804..1ec945958c 100644
--- a/core/tests/Drupal/Setup/Commands/TestInstallationSetupApplication.php
+++ b/core/tests/Drupal/Setup/Commands/TestInstallationSetupApplication.php
@@ -35,7 +35,7 @@ public function __construct($autoloader) {
   protected function getDefaultCommands() {
     // Even though this is a single command, keep the HelpCommand (--help).
     $default_commands = parent::getDefaultCommands();
-    $default_commands[] = new TestInstallationSetupCommand($this->autoloader);
+    $default_commands[] = new TestInstallationSetupCommand();
     $default_commands[] = new TestTeardownCommand($this->autoloader);
     return $default_commands;
   }
diff --git a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
index 9262499a72..8e01727fcf 100644
--- a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
+++ b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
@@ -2,8 +2,6 @@
 
 namespace Drupal\Setup\Commands;
 
-use Drupal\Core\DrupalKernel;
-use Drupal\Core\Site\Settings;
 use Drupal\Core\Test\FunctionalTestSetupTrait;
 use Drupal\Core\Test\TestSetupTrait;
 use Drupal\Setup\TestSetupInterface;
@@ -13,7 +11,6 @@
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
-use Symfony\Component\HttpFoundation\Request;
 
 /**
  * Symfony console command to setup Drupal.
@@ -58,28 +55,6 @@ class TestInstallationSetupCommand extends Command {
    */
   protected $langcode = 'en';
 
-  /**
-   * The used PHP autoloader.
-   *
-   * @var object
-   */
-  protected $autoloader;
-
-  /**
-   * Constructs a new TestInstallationSetupCommand.
-   *
-   * @param string $autoloader
-   *   The used PHP autoloader.
-   * @param string|null $name
-   *   The name of the command. Passing NULL means it must be set in
-   *   configure().
-   */
-  public function __construct($autoloader, $name = NULL) {
-    parent::__construct($name);
-
-    $this->autoloader = $autoloader;
-  }
-
   /**
    * {@inheritdoc}
    */
@@ -96,13 +71,14 @@ protected function configure() {
    * {@inheritdoc}
    */
   protected function execute(InputInterface $input, OutputInterface $output) {
+    // Validate the setup class prior to installing a database to avoid creating
+    // unnecessary sites.
+    $this->validateSetupClass($input->getOption('setup_class'));
     $db_url = $input->getOption('db_url');
     $base_url = $input->getOption('base_url');
     putenv("SIMPLETEST_DB=$db_url");
     putenv("SIMPLETEST_BASE_URL=$base_url");
 
-    $this->bootstrapDrupal();
-
     // Manage site fixture.
     $this->setup($input->getOption('install_profile'), $input->getOption('setup_class'), $input->getOption('langcode'));
 
@@ -113,18 +89,26 @@ protected function execute(InputInterface $input, OutputInterface $output) {
   }
 
   /**
-   * Bootstraps the drupal kernel.
+   * Validates the setup class.
+   *
+   * @param string|null $class
+   *   The setup class to validate.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the class does not exist or does not implement
+   *   TestSetupInterface.
    */
-  protected function bootstrapDrupal() {
-    $request = Request::createFromGlobals();
-    $kernel = DrupalKernel::createFromRequest($request, $this->autoloader, $this->getApplication()->getName());
-    DrupalKernel::bootEnvironment($kernel->getAppRoot());
-
-    Settings::initialize(
-      dirname(dirname(dirname(dirname(__DIR__)))),
-      DrupalKernel::findSitePath($request),
-      $this->autoloader
-    );
+  protected function validateSetupClass($class) {
+    if ($class === NULL) {
+      return;
+    }
+    if (!class_exists($class)) {
+      throw new \InvalidArgumentException("There was a problem loading {$class}");
+    }
+
+    if (!is_subclass_of($class, TestSetupInterface::class)) {
+      throw new \InvalidArgumentException(sprintf('You need to define a class implementing \Drupal\Setup\TestSetupInterface'));
+    }
   }
 
   /**
@@ -175,14 +159,6 @@ protected function installDrupal() {
    * @see \Drupal\Setup\TestSetupInterface
    */
   protected function executeSetupClass($class) {
-    if (!class_exists($class)) {
-      throw new \InvalidArgumentException("There was a problem loading {$class}");
-    }
-
-    if (!is_subclass_of($class, TestSetupInterface::class)) {
-      throw new \InvalidArgumentException(sprintf('You need to define a class implementing \Drupal\Setup\TestSetupInterface'));
-    }
-
     /** @var \Drupal\Setup\TestSetupInterface $instance */
     $instance = new $class();
     $instance->setup();
diff --git a/core/tests/Drupal/Setup/Commands/TestTeardownCommand.php b/core/tests/Drupal/Setup/Commands/TestTeardownCommand.php
index 4b8aef8841..cfec6c558c 100644
--- a/core/tests/Drupal/Setup/Commands/TestTeardownCommand.php
+++ b/core/tests/Drupal/Setup/Commands/TestTeardownCommand.php
@@ -4,9 +4,9 @@
 
 use Drupal\Core\Database\Database;
 use Drupal\Core\DrupalKernel;
-use Drupal\Core\Site\Settings;
 use Drupal\Core\Test\TestDatabase;
 use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
@@ -46,7 +46,7 @@ public function __construct($autoloader, $name = NULL) {
    */
   protected function configure() {
     $this->setName('teardown-drupal-test')
-      ->addArgument('db_prefix')
+      ->addArgument('db_prefix', InputArgument::REQUIRED, 'The database prefix for the test site')
       ->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'));
   }
@@ -61,22 +61,33 @@ protected function execute(InputInterface $input, OutputInterface $output) {
     putenv("SIMPLETEST_DB=$db_url");
     putenv("SIMPLETEST_BASE_URL=$base_url");
 
-    $this->bootstrapDrupal($db_prefix);
+    $kernel = $this->bootstrapDrupal();
 
     // Handle the cleanup of the test site.
-    $this->teardown($db_prefix);
+    $this->teardown($db_prefix, $db_url, $kernel->getAppRoot());
   }
 
   /**
-   * Removes a given instance by deleting all the database tables.
+   * Removes a given instance by deleting all the database tables and files.
    *
    * @param string $db_prefix
    *   The used database prefix.
+   * @param $db_url
+   *   The database URL.
+   * @param $app_root
+   *   The app root.
    */
-  public function teardown($db_prefix) {
-    $tables = Database::getConnection()->schema()->findTables('%');
+  public function teardown($db_prefix, $db_url, $app_root) {
+    // Connect to the test database.
+    $database = Database::convertDbUrlToConnectionInfo($db_url, $app_root);
+    $database['prefix'] = ['default' => $db_prefix];
+    Database::addConnectionInfo(__CLASS__, 'default', $database);
+
+    // Remove all the tables.
+    $connection = Database::getConnection('default', __CLASS__);
+    $tables = $connection->schema()->findTables('%');
     foreach ($tables as $table) {
-      if (Database::getConnection()->schema()->dropTable($table)) {
+      if ($connection->schema()->dropTable($table)) {
         unset($tables[$table]);
       }
     }
@@ -107,21 +118,18 @@ public static function filePreDeleteCallback($path) {
   /**
    * Bootstraps the drupal kernel.
    *
-   * @param string $db_prefix
-   *   The database prefix.
+   * @return \Drupal\Core\DrupalKernel
+   *   The Drupal kernel.
    */
-  protected function bootstrapDrupal($db_prefix) {
+  protected function bootstrapDrupal() {
     $request = Request::createFromGlobals();
-    $_COOKIE['SIMPLETEST_USER_AGENT'] = drupal_generate_test_ua($db_prefix);
-
     $kernel = DrupalKernel::createFromRequest($request, $this->autoloader, $this->getApplication()->getName());
-    DrupalKernel::bootEnvironment($kernel->getAppRoot());
 
-    Settings::initialize(
-      dirname(dirname(dirname(dirname(__DIR__)))),
-      DrupalKernel::findSitePath($request),
-      $this->autoloader
-    );
+    // Finish booting Drupal in order to use functions like
+    // file_unmanaged_delete_recursive().
+    $kernel->boot();
+    $kernel->loadLegacyIncludes();
+    return $kernel;
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Setup/Commands/SetupDrupalTestScriptTest.php b/core/tests/Drupal/Tests/Setup/Commands/SetupDrupalTestScriptTest.php
new file mode 100644
index 0000000000..20fe0a7932
--- /dev/null
+++ b/core/tests/Drupal/Tests/Setup/Commands/SetupDrupalTestScriptTest.php
@@ -0,0 +1,189 @@
+<?php
+
+namespace Drupal\Tests\Setup\Commands;
+
+use Drupal\Core\Database\Database;
+use Drupal\Core\Test\TestDatabase;
+use Drupal\Setup\SetupDrupalTestScript;
+use Drupal\Tests\UnitTestCase;
+use GuzzleHttp\Client;
+use GuzzleHttp\Psr7\Request;
+use Symfony\Component\Process\PhpExecutableFinder;
+use Symfony\Component\Process\Process;
+
+/**
+ * Tests setup-drupal-test.php.
+ *
+ * @group Setup
+ *
+ * This test uses the Drupal\Core\Database\Database class which has a static.
+ * Therefore run in an separate process to avoid side effects.
+ *
+ * @runTestsInSeparateProcesses
+ * @preserveGlobalState disabled
+ *
+ * @see \Drupal\Setup\Commands\TestInstallationSetupApplication
+ * @see \Drupal\Setup\Commands\TestInstallationSetupCommand
+ * @see \Drupal\Setup\Commands\TestTeardownCommand
+ */
+class SetupDrupalTestScriptTest extends UnitTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->root = dirname(dirname(substr(__DIR__, 0, -strlen(__NAMESPACE__))));
+  }
+
+  /**
+   * @coversNothing
+   */
+  public function testInstallWithNonExistingClass() {
+    $phpBinaryFinder = new PhpExecutableFinder();
+    $phpBinaryPath = $phpBinaryFinder->find();
+
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php setup-drupal-test --setup_class "this-class-does-not-exist" --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->run();
+
+    $this->assertContains('There was a problem loading this-class-does-not-exist', $process->getErrorOutput());
+    $this->assertSame(1, $process->getExitCode());
+  }
+
+  /**
+   * @coversNothing
+   */
+  public function testInstallWithNonSetupClass() {
+    $phpBinaryFinder = new PhpExecutableFinder();
+    $phpBinaryPath = $phpBinaryFinder->find();
+
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php setup-drupal-test --setup_class "' . static::class . '" --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->run();
+
+    $this->assertContains('You need to define a class implementing \Drupal\Setup\TestSetupInterface', $process->getErrorOutput());
+    $this->assertSame(1, $process->getExitCode());
+  }
+
+  /**
+   * @coversNothing
+   */
+  public function testInstallScript() {
+    $phpBinaryFinder = new PhpExecutableFinder();
+    $phpBinaryPath = $phpBinaryFinder->find();
+
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php setup-drupal-test --setup_class "' . SetupDrupalTestScript::class . '" --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->setTimeout(500);
+    $process->run();
+
+    $this->assertSame(0, $process->getExitCode());
+    $result = json_decode($process->getOutput(), TRUE);
+    $db_prefix = $result['db_prefix'];
+    $this->assertStringStartsWith('simpletest' . substr($db_prefix, 4) . ':', $result['user_agent']);
+
+    $http_client = new Client();
+    $request = (new Request('GET', getenv('SIMPLETEST_BASE_URL') . '/test-page'))
+      ->withHeader('User-Agent', trim($result['user_agent']));
+
+    $response = $http_client->send($request);
+    // Ensure the test_page_test module got installed.
+    $this->assertContains('Test page | Drupal', (string) $response->getBody());
+
+    // Ensure that there are files and database tables for teardown to clean up.
+    $key = $this->addTestDatabase($db_prefix);
+    $this->assertGreaterThan(0, count(Database::getConnection('default', $key)->schema()->findTables('%')));
+    $test_database = new TestDatabase($db_prefix);
+    $test_file = $test_database->getTestSitePath() . DIRECTORY_SEPARATOR . '.htkey';
+    $this->assertFileExists($test_file);
+
+    // Install another site so we can ensure tear down only removes one site at
+    // a time.
+    $process->run();
+    $result = json_decode($process->getOutput(), TRUE);
+    $other_db_prefix = $result['db_prefix'];
+    $other_key = $this->addTestDatabase($other_db_prefix);
+    $this->assertGreaterThan(0, count(Database::getConnection('default', $other_key)->schema()->findTables('%')));
+
+    // Now test the tear down process as well.
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php teardown-drupal-test ' . $db_prefix . ' --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->setTimeout(500);
+    $process->run();
+    $this->assertSame(0, $process->getExitCode());
+
+    // Ensure that all the tables and files for this DB prefix are gone.
+    $this->assertCount(0, Database::getConnection('default', $key)->schema()->findTables('%'));
+    $this->assertFileNotExists($test_file);
+
+    // Ensure the other sites tables and files still exist.
+    $this->assertGreaterThan(0, count(Database::getConnection('default', $other_key)->schema()->findTables('%')));
+    $test_database = new TestDatabase($other_db_prefix);
+    $test_file = $test_database->getTestSitePath() . DIRECTORY_SEPARATOR . '.htkey';
+    $this->assertFileExists($test_file);
+
+    // Now test the tear down process as well.
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php teardown-drupal-test ' . $other_db_prefix . ' --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->setTimeout(500);
+    $process->run();
+    $this->assertSame(0, $process->getExitCode());
+
+    $this->assertCount(0, Database::getConnection('default', $other_key)->schema()->findTables('%'));
+    $this->assertFileNotExists($test_file);
+  }
+
+  /**
+   * @coversNothing
+   */
+  public function testInstallInDifferentLanguage() {
+    $phpBinaryFinder = new PhpExecutableFinder();
+    $phpBinaryPath = $phpBinaryFinder->find();
+
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php setup-drupal-test --langcode fr --setup_class "' . SetupDrupalTestScript::class . '" --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->setTimeout(500);
+    $process->run();
+    $this->assertEquals(0, $process->getExitCode());
+
+    $result = json_decode($process->getOutput(), TRUE);
+    $db_prefix = $result['db_prefix'];
+    $http_client = new Client();
+    $request = (new Request('GET', getenv('SIMPLETEST_BASE_URL') . '/test-page'))
+      ->withHeader('User-Agent', trim($result['user_agent']));
+
+    $response = $http_client->send($request);
+    // Ensure the test_page_test module got installed.
+    $this->assertContains('Test page | Drupal', (string) $response->getBody());
+    $this->assertContains('lang="fr"', (string) $response->getBody());
+
+    // Now test the tear down process as well.
+    $command_line = $phpBinaryPath . ' core/scripts/setup-drupal-test.php teardown-drupal-test ' . $db_prefix . ' --db_url "' . getenv('SIMPLETEST_DB') . '"';
+    $process = new Process($command_line, $this->root);
+    $process->setTimeout(500);
+    $process->run();
+    $this->assertSame(0, $process->getExitCode());
+
+    // Ensure that all the tables for this DB prefix are gone.
+    $this->assertCount(0, Database::getConnection('default', $this->addTestDatabase($db_prefix))->schema()->findTables('%'));
+  }
+
+  /**
+   * Adds the installed test site to the database connection info.
+   *
+   * @param $db_prefix
+   *   The prefix of the installed test site.
+   *
+   * @return string
+   *   The database key of the added connection.
+   */
+  protected function addTestDatabase($db_prefix) {
+    $database = Database::convertDbUrlToConnectionInfo(getenv('SIMPLETEST_DB'), $this->root);
+    $database['prefix'] = ['default' => $db_prefix];
+    $target = __CLASS__ . $db_prefix;
+    Database::addConnectionInfo($target, 'default', $database);
+    return $target;
+  }
+
+}