class KernelTestBase

abstract class KernelTestBase extends TestCase implements ServiceProviderInterface {
    use AssertContentTrait;
    use RandomGeneratorTrait;
    use ConfigTestTrait;
    use ExtensionListTestTrait;
    use TestRequirementsTrait;
    use PhpUnitCompatibilityTrait;
    use ProphecyTrait;
    use ExpectDeprecationTrait;
    
    /**
     * {@inheritdoc}
     *
     * Back up and restore static class properties that may be changed by tests.
     *
     * @see self::runTestInSeparateProcess
     */
    protected $backupStaticAttributes = TRUE;
    
    /**
     * {@inheritdoc}
     */
    public function __construct(string $name) {
        parent::__construct($name);
        $this->setRunTestInSeparateProcess(TRUE);
    }
    
    /**
     * {@inheritdoc}
     *
     * Contains a few static class properties for performance.
     */
    protected $backupStaticAttributesBlacklist = [
        // Ignore static discovery/parser caches to speed up tests.
'Drupal\\Component\\Discovery\\YamlDiscovery' => [
            'parsedFiles',
        ],
        'Drupal\\Core\\DependencyInjection\\YamlFileLoader' => [
            'yaml',
        ],
        'Drupal\\Core\\Extension\\ExtensionDiscovery' => [
            'files',
        ],
        'Drupal\\Core\\Extension\\InfoParser' => [
            'parsedInfos',
        ],
        // Drupal::$container cannot be serialized.
'Drupal' => [
            'container',
        ],
        // Settings cannot be serialized.
'Drupal\\Core\\Site\\Settings' => [
            'instance',
        ],
    ];
    
    /**
     * @var \Composer\Autoload\Classloader
     */
    protected $classLoader;
    
    /**
     * @var string
     */
    protected $siteDirectory;
    
    /**
     * @var string
     */
    protected $databasePrefix;
    
    /**
     * @var \Drupal\Core\DependencyInjection\ContainerBuilder
     */
    protected $container;
    
    /**
     * Modules to install.
     *
     * The test runner will merge the $modules lists from this class, the class
     * it extends, and so on up the class hierarchy. It is not necessary to
     * include modules in your list that a parent class has already declared.
     *
     * @var array
     *
     * @see \Drupal\Tests\KernelTestBase::enableModules()
     * @see \Drupal\Tests\KernelTestBase::bootKernel()
     */
    protected static $modules = [];
    
    /**
     * The virtual filesystem root directory.
     *
     * @var \org\bovigo\vfs\vfsStreamDirectory
     */
    protected $vfsRoot;
    
    /**
     * @var \Drupal\Core\Config\ConfigImporter
     *
     * @todo Move into Config test base class.
     */
    protected $configImporter;
    
    /**
     * The key_value service that must persist between container rebuilds.
     *
     * @var \Drupal\Core\KeyValueStore\KeyValueMemoryFactory
     */
    protected KeyValueMemoryFactory $keyValue;
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * Set to TRUE to strict check all configuration saved.
     *
     * @var bool
     *
     * @see \Drupal\Core\Config\Development\ConfigSchemaChecker
     */
    protected $strictConfigSchema = TRUE;
    
    /**
     * An array of config object names that are excluded from schema checking.
     *
     * @var string[]
     */
    protected static $configSchemaCheckerExclusions = [
        // Following are used to test lack of or partial schema. Where partial
        // schema is provided, that is explicitly tested in specific tests.
'config_schema_test.no_schema',
        'config_schema_test.some_schema',
        'config_schema_test.schema_data_types',
        'config_schema_test.no_schema_data_types',
        // Used to test application of schema to filtering of configuration.
'config_test.dynamic.system',
    ];
    
    /**
     * Set to TRUE to make user 1 a super user.
     *
     * @var bool
     *
     * @see \Drupal\Core\Session\SuperUserAccessPolicy
     */
    protected bool $usesSuperUserAccessPolicy;
    
    /**
     * {@inheritdoc}
     */
    public static function setUpBeforeClass() : void {
        parent::setUpBeforeClass();
        VarDumper::setHandler(TestVarDumper::class . '::cliHandler');
    }
    
    /**
     * {@inheritdoc}
     */
    protected function setUp() : void {
        parent::setUp();
        // Allow tests to compare MarkupInterface objects via assertEquals().
        $this->registerComparator(new MarkupInterfaceComparator());
        $this->root = static::getDrupalRoot();
        chdir($this->root);
        $this->initFileCache();
        $this->bootEnvironment();
        $this->bootKernel();
    }
    
    /**
     * Bootstraps a basic test environment.
     *
     * Should not be called by tests. Only visible for DrupalKernel integration
     * tests.
     *
     * @see \Drupal\KernelTests\Core\DrupalKernel\DrupalKernelTest
     * @internal
     */
    protected function bootEnvironment() {
        \Drupal::unsetContainer();
        $this->classLoader = (require $this->root . '/autoload.php');
        // Set up virtual filesystem.
        Database::addConnectionInfo('default', 'test-runner', $this->getDatabaseConnectionInfo()['default']);
        $test_db = new TestDatabase();
        $this->siteDirectory = $test_db->getTestSitePath();
        // Ensure that all code that relies on drupal_valid_test_ua() can still be
        // safely executed. This primarily affects the (test) site directory
        // resolution (used by e.g. LocalStream and PhpStorage).
        $this->databasePrefix = $test_db->getDatabasePrefix();
        drupal_valid_test_ua($this->databasePrefix);
        $settings = [
            'hash_salt' => static::class,
            'file_public_path' => $this->siteDirectory . '/files',
            // Disable Twig template caching/dumping.
'twig_cache' => FALSE,
        ];
        new Settings($settings);
        $this->setUpFilesystem();
        foreach (Database::getAllConnectionInfo() as $key => $targets) {
            Database::removeConnection($key);
        }
        Database::addConnectionInfo('default', 'default', $this->getDatabaseConnectionInfo()['default']);
    }
    
    /**
     * Sets up the filesystem, so things like the file directory.
     */
    protected function setUpFilesystem() {
        $test_db = new TestDatabase($this->databasePrefix);
        $test_site_path = $test_db->getTestSitePath();
        $this->vfsRoot = vfsStream::setup('root');
        $this->vfsRoot
            ->addChild(vfsStream::newDirectory($test_site_path));
        $this->siteDirectory = vfsStream::url('root/' . $test_site_path);
        mkdir($this->siteDirectory . '/files', 0775);
        mkdir($this->siteDirectory . '/files/config/sync', 0775, TRUE);
        $settings = Settings::getInstance() ? Settings::getAll() : [];
        $settings['file_public_path'] = $this->siteDirectory . '/files';
        $settings['config_sync_directory'] = $this->siteDirectory . '/files/config/sync';
        new Settings($settings);
    }
    
    /**
     * @return string
     */
    public function getDatabasePrefix() {
        return $this->databasePrefix;
    }
    
    /**
     * Bootstraps a kernel for a test.
     */
    protected function bootKernel() {
        $this->setSetting('container_yamls', []);
        // Allow for test-specific overrides.
        $settings_services_file = $this->root . '/sites/default/testing.services.yml';
        if (file_exists($settings_services_file)) {
            // Copy the testing-specific service overrides in place.
            $testing_services_file = $this->siteDirectory . '/services.yml';
            copy($settings_services_file, $testing_services_file);
            $this->setSetting('container_yamls', [
                $testing_services_file,
            ]);
        }
        // Allow for global test environment overrides.
        if (file_exists($test_env = $this->root . '/sites/default/testing.services.yml')) {
            $GLOBALS['conf']['container_yamls']['testing'] = $test_env;
        }
        // Add this test class as a service provider.
        $GLOBALS['conf']['container_service_providers']['test'] = $this;
        $modules = self::getModulesToEnable(static::class);
        // When a module is providing the database driver, then enable that module.
        $connection_info = Database::getConnectionInfo();
        $namespace = $connection_info['default']['namespace'] ?? '';
        $autoload = $connection_info['default']['autoload'] ?? '';
        if (str_contains($autoload, 'src/Driver/Database/')) {
            [
                $first,
                $second,
            ] = explode('\\', $namespace, 3);
            if ($first === 'Drupal' && strtolower($second) === $second) {
                // Add the module that provides the database driver to the list of
                // modules as the first to be enabled.
                array_unshift($modules, $second);
            }
        }
        // Bootstrap the kernel. Do not use createFromRequest() to retain Settings.
        $kernel = new DrupalKernel('testing', $this->classLoader, FALSE);
        $kernel->setSitePath($this->siteDirectory);
        // Boot a new one-time container from scratch. Set the module list upfront
        // to avoid a subsequent rebuild or setting the kernel into the
        // pre-installer mode.
        $extensions = $modules ? $this->getExtensionsForModules($modules) : [];
        $kernel->updateModules($extensions, $extensions);
        // DrupalKernel::boot() is not sufficient as it does not invoke preHandle(),
        // which is required to initialize legacy global variables.
        $request = Request::create('/');
        $kernel->boot();
        $request->attributes
            ->set(RouteObjectInterface::ROUTE_OBJECT, new Route('<none>'));
        $request->attributes
            ->set(RouteObjectInterface::ROUTE_NAME, '<none>');
        $kernel->preHandle($request);
        $this->container = $kernel->getContainer();
        // Run database tasks and check for errors.
        $installer_class = $namespace . "\\Install\\Tasks";
        $errors = (new $installer_class())->runTasks();
        if (!empty($errors)) {
            $this->fail('Failed to run installer database tasks: ' . implode(', ', $errors));
        }
        // Setup the destination to the be frontpage by default.
        \Drupal::destination()->set('/');
        // Write the core.extension configuration.
        // Required for ConfigInstaller::installDefaultConfig() to work.
        $this->container
            ->get('config.storage')
            ->write('core.extension', [
            'module' => array_fill_keys($modules, 0),
            'theme' => [],
        ]);
        $settings = Settings::getAll();
        $settings['php_storage']['default'] = [
            'class' => '\\Drupal\\Component\\PhpStorage\\FileStorage',
        ];
        new Settings($settings);
        // Manually configure the test mail collector implementation to prevent
        // tests from sending out emails and collect them in state instead.
        // While this should be enforced via settings.php prior to installation,
        // some tests expect to be able to test mail system implementations.
        $GLOBALS['config']['system.mail']['interface']['default'] = 'test_mail_collector';
        $GLOBALS['config']['system.mail']['mailer_dsn'] = [
            'scheme' => 'null',
            'host' => 'null',
            'user' => NULL,
            'password' => NULL,
            'port' => NULL,
            'options' => [],
        ];
        // Manually configure the default file scheme so that modules that use file
        // functions don't have to install system and its configuration.
        // @see file_default_scheme()
        $GLOBALS['config']['system.file']['default_scheme'] = 'public';
    }
    
    /**
     * Configuration accessor for tests. Returns non-overridden configuration.
     *
     * @param string $name
     *   The configuration name.
     *
     * @return \Drupal\Core\Config\Config
     *   The configuration object with original configuration data.
     */
    protected function config($name) {
        return $this->container
            ->get('config.factory')
            ->getEditable($name);
    }
    
    /**
     * Returns the Database connection info to be used for this test.
     *
     * This method only exists for tests of the Database component itself, because
     * they require multiple database connections. Each SQLite :memory: connection
     * creates a new/separate database in memory. A shared-memory SQLite file URI
     * triggers PHP open_basedir/allow_url_fopen/allow_url_include restrictions.
     * Due to that, Database tests are running against a SQLite database that is
     * located in an actual file in the system's temporary directory.
     *
     * Other tests should not override this method.
     *
     * @return array
     *   A Database connection info array.
     *
     * @internal
     */
    protected function getDatabaseConnectionInfo() {
        // If the test is run with argument dburl then use it.
        $db_url = getenv('SIMPLETEST_DB');
        if (empty($db_url)) {
            throw new \Exception('There is no database connection so no tests can be run. You must provide a SIMPLETEST_DB environment variable to run PHPUnit based functional tests outside of run-tests.sh. See https://www.drupal.org/node/2116263#skipped-tests for more information.');
        }
        else {
            $database = Database::convertDbUrlToConnectionInfo($db_url, $this->root, TRUE);
            Database::addConnectionInfo('default', 'default', $database);
        }
        // Clone the current connection and replace the current prefix.
        $connection_info = Database::getConnectionInfo('default');
        if (!empty($connection_info)) {
            Database::renameConnection('default', 'simpletest_original_default');
            foreach ($connection_info as $target => $value) {
                // Replace the full table prefix definition to ensure that no table
                // prefixes of the test runner leak into the test.
                $connection_info[$target]['prefix'] = $this->databasePrefix;
            }
        }
        return $connection_info;
    }
    
    /**
     * Initializes the FileCache component.
     *
     * We can not use the Settings object in a component, that's why we have to do
     * it here instead of \Drupal\Component\FileCache\FileCacheFactory.
     */
    protected function initFileCache() {
        $configuration = Settings::get('file_cache');
        // Provide a default configuration, if not set.
        if (!isset($configuration['default'])) {
            // @todo Use extension_loaded('apcu') for non-testbot
            //   https://www.drupal.org/node/2447753.
            if (function_exists('apcu_fetch')) {
                $configuration['default']['cache_backend_class'] = ApcuFileCacheBackend::class;
            }
        }
        FileCacheFactory::setConfiguration($configuration);
        FileCacheFactory::setPrefix(Settings::getApcuPrefix('file_cache', $this->root));
    }
    
    /**
     * Returns Extension objects for $modules to install.
     *
     * @param string[] $modules
     *   The list of modules to install.
     *
     * @return \Drupal\Core\Extension\Extension[]
     *   Extension objects for $modules, keyed by module name.
     *
     * @throws \PHPUnit\Framework\Exception
     *   If a module is not available.
     *
     * @see \Drupal\Tests\KernelTestBase::enableModules()
     * @see \Drupal\Core\Extension\ModuleHandler::add()
     */
    private function getExtensionsForModules(array $modules) : array {
        $extensions = [];
        $discovery = new ExtensionDiscovery($this->root);
        $discovery->setProfileDirectories([]);
        $list = $discovery->scan('module');
        foreach ($modules as $name) {
            if (!isset($list[$name])) {
                throw new Exception("Unavailable module: '{$name}'. If this module needs to be downloaded for testing, include it in the 'require-dev' section of your composer.json file.");
            }
            $extensions[$name] = $list[$name];
        }
        return $extensions;
    }
    
    /**
     * Registers test-specific services.
     *
     * Extend this method in your test to register additional services. This
     * method is called whenever the kernel is rebuilt.
     *
     * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container
     *   The service container to enhance.
     *
     * @see \Drupal\Tests\KernelTestBase::bootKernel()
     */
    public function register(ContainerBuilder $container) {
        // Keep the container object around for tests.
        $this->container = $container;
        $container->register('datetime.time', 'Drupal\\Component\\Datetime\\Time');
        $container->register('flood', 'Drupal\\Core\\Flood\\MemoryBackend')
            ->addArgument(new Reference('request_stack'));
        $container->register('lock', 'Drupal\\Core\\Lock\\NullLockBackend');
        $container->register('cache_factory', 'Drupal\\Core\\Cache\\MemoryBackendFactory')
            ->addArgument(new Reference('datetime.time'));
        // Disable the super user access policy so that we are sure our tests check
        // for the right permissions.
        if (!isset($this->usesSuperUserAccessPolicy)) {
            $test_file_name = (new \ReflectionClass($this))->getFileName();
            // @todo Decide in https://www.drupal.org/project/drupal/issues/3437926
            //   how to remove this fallback behavior.
            $this->usesSuperUserAccessPolicy = !str_starts_with($test_file_name, $this->root . DIRECTORY_SEPARATOR . 'core');
        }
        $container->setParameter('security.enable_super_user', $this->usesSuperUserAccessPolicy);
        // Use memory for key value storages to avoid database queries. Store the
        // key value factory on the test object so that key value storages persist
        // container rebuilds, otherwise all state data would vanish.
        if (!isset($this->keyValue)) {
            $this->keyValue = new KeyValueMemoryFactory();
        }
        $container->set('keyvalue', $this->keyValue);
        $container->getDefinition('keyvalue')
            ->setSynthetic(TRUE);
        // Set the default language on the minimal container.
        $container->setParameter('language.default_values', Language::$defaultValues);
        // Determine whether the test is a core test.
        $test_file_name = (new \ReflectionClass($this))->getFileName();
        // @todo Decide in https://www.drupal.org/project/drupal/issues/3395099 when/how to trigger deprecation errors or even failures for contrib modules.
        $is_core_test = str_starts_with($test_file_name, $this->root . DIRECTORY_SEPARATOR . 'core');
        if ($this->strictConfigSchema) {
            $container->register('testing.config_schema_checker', ConfigSchemaChecker::class)
                ->addArgument(new Reference('config.typed'))
                ->addArgument($this->getConfigSchemaExclusions())
                ->addArgument($is_core_test)
                ->addTag('event_subscriber');
        }
        // Add event subscriber to check that an entity schema is installed before
        // any field storages are created on the entity.
        $container->register('testing.field_storage_create_check', FieldStorageCreateCheckSubscriber::class)
            ->addArgument(new Reference('database'))
            ->addArgument(new Reference('entity_type.manager'))
            ->addArgument($is_core_test)
            ->addTag('event_subscriber');
        // Relax the password hashing cost in tests to avoid performance issues.
        if ($container->hasDefinition('password')) {
            $container->getDefinition('password')
                ->setArguments([
                PASSWORD_BCRYPT,
                [
                    'cost' => 4,
                ],
            ]);
        }
        // Add the on demand rebuild route provider service.
        $route_provider_service_name = 'router.route_provider';
        // While $container->get() does a recursive resolve, getDefinition() does
        // not, so do it ourselves.
        $id = $route_provider_service_name;
        while ($container->hasAlias($id)) {
            $id = (string) $container->getAlias($id);
        }
        $definition = $container->getDefinition($id);
        $definition->clearTag('needs_destruction');
        $container->setDefinition("test.{$route_provider_service_name}", $definition);
        $route_provider_definition = new Definition(RouteProvider::class);
        $route_provider_definition->setPublic(TRUE);
        $container->setDefinition($id, $route_provider_definition);
        // Remove the stored configuration importer so if used again it will be
        // built with up-to-date services.
        $this->configImporter = NULL;
    }
    
    /**
     * Gets the config schema exclusions for this test.
     *
     * @return string[]
     *   An array of config object names that are excluded from schema checking.
     */
    protected function getConfigSchemaExclusions() {
        $class = static::class;
        $exceptions = [];
        while ($class) {
            if (property_exists($class, 'configSchemaCheckerExclusions')) {
                $exceptions = array_merge($exceptions, $class::$configSchemaCheckerExclusions);
            }
            $class = get_parent_class($class);
        }
        // Filter out any duplicates.
        return array_unique($exceptions);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function assertPostConditions() : void {
        // Execute registered Drupal shutdown functions prior to tearing down.
        // @see _drupal_shutdown_function()
        $callbacks =& drupal_register_shutdown_function();
        while ($callback = array_shift($callbacks)) {
            call_user_func_array($callback['callback'], $callback['arguments']);
        }
        // Shut down the kernel (if bootKernel() was called).
        // @see \Drupal\KernelTests\Core\DrupalKernel\DrupalKernelTest
        if ($this->container) {
            $this->container
                ->get('kernel')
                ->shutdown();
        }
        parent::assertPostConditions();
    }
    
    /**
     * {@inheritdoc}
     */
    protected function tearDown() : void {
        if ($this->container) {
            // Clean up mock session started in DrupalKernel::preHandle().
            
            /** @var \Symfony\Component\HttpFoundation\Session\Session $session */
            $session = $this->container
                ->get('request_stack')
                ->getSession();
            $session->clear();
            $session->save();
        }
        // Destroy the testing kernel.
        if (isset($this->kernel)) {
            $this->kernel
                ->shutdown();
        }
        // Remove all prefixed tables.
        $original_connection_info = Database::getConnectionInfo('simpletest_original_default');
        $original_prefix = $original_connection_info['default']['prefix'] ?? NULL;
        $test_connection_info = Database::getConnectionInfo('default');
        $test_prefix = $test_connection_info['default']['prefix'] ?? NULL;
        if ($original_prefix != $test_prefix) {
            $tables = Database::getConnection()->schema()
                ->findTables('%');
            foreach ($tables as $table) {
                if (Database::getConnection()->schema()
                    ->dropTable($table)) {
                    unset($tables[$table]);
                }
            }
        }
        // Free up memory: Own properties.
        $this->classLoader = NULL;
        $this->vfsRoot = NULL;
        $this->configImporter = NULL;
        // Clean FileCache cache.
        FileCache::reset();
        // Clean up statics, container, and settings.
        if (function_exists('drupal_static_reset')) {
            drupal_static_reset();
        }
        \Drupal::unsetContainer();
        $this->container = NULL;
        new Settings([]);
        parent::tearDown();
    }
    
    /**
     * Additional tear down method to close the connection at the end.
     */
    public function tearDownCloseDatabaseConnection() {
        // Destroy the database connection, which for example removes the memory
        // from sqlite in memory.
        foreach (Database::getAllConnectionInfo() as $key => $targets) {
            Database::removeConnection($key);
        }
    }
    
    /**
     * Installs default configuration for a given list of modules.
     *
     * @param string|string[] $modules
     *   A module or list of modules for which to install default configuration.
     *
     * @throws \LogicException
     *   If any module in $modules is not enabled.
     */
    protected function installConfig($modules) {
        foreach ((array) $modules as $module) {
            if (!$this->container
                ->get('module_handler')
                ->moduleExists($module)) {
                throw new \LogicException("{$module} module is not installed.");
            }
            try {
                $this->container
                    ->get('config.installer')
                    ->installDefaultConfig('module', $module);
            } catch (\Exception $e) {
                throw new \Exception(sprintf('Exception when installing config for module %s, message was: %s', $module, $e->getMessage()), 0, $e);
            }
        }
    }
    
    /**
     * Installs database tables from a module schema definition.
     *
     * @param string $module
     *   The name of the module that defines the table's schema.
     * @param string|array $tables
     *   The name or an array of the names of the tables to install.
     *
     * @throws \LogicException
     *   If $module is not enabled or the table schema cannot be found.
     */
    protected function installSchema($module, $tables) {
        
        /** @var \Drupal\Core\Extension\ModuleHandlerInterface $module_handler */
        $module_handler = $this->container
            ->get('module_handler');
        // Database connection schema is technically able to create database tables
        // using any valid specification, for example of a non-enabled module. But
        // ability to load the module's .install file depends on many other factors.
        // To prevent differences in test behavior and non-reproducible test
        // failures, we only allow the schema of explicitly loaded/enabled modules
        // to be installed.
        if (!$module_handler->moduleExists($module)) {
            throw new \LogicException("{$module} module is not installed.");
        }
        $specification = SchemaInspector::getTablesSpecification($module_handler, $module);
        
        /** @var \Drupal\Core\Database\Schema $schema */
        $schema = $this->container
            ->get('database')
            ->schema();
        $tables = (array) $tables;
        foreach ($tables as $table) {
            if ($module === 'system' && $table === 'sequences') {
                @trigger_error('Installing the table sequences with the method KernelTestBase::installSchema() is deprecated in drupal:10.2.0 and is removed from drupal:12.0.0. See https://www.drupal.org/node/3349345', E_USER_DEPRECATED);
            }
            if (empty($specification[$table])) {
                throw new \LogicException("{$module} module does not define a schema for table '{$table}'.");
            }
            $schema->createTable($table, $specification[$table]);
        }
    }
    
    /**
     * Installs the storage schema for a specific entity type.
     *
     * @param string $entity_type_id
     *   The ID of the entity type.
     */
    protected function installEntitySchema($entity_type_id) {
        $entity_type_manager = \Drupal::entityTypeManager();
        $entity_type = $entity_type_manager->getDefinition($entity_type_id);
        \Drupal::service('entity_type.listener')->onEntityTypeCreate($entity_type);
        // For test runs, the most common storage backend is a SQL database. For
        // this case, ensure the tables got created.
        $storage = $entity_type_manager->getStorage($entity_type_id);
        if ($storage instanceof SqlEntityStorageInterface) {
            $tables = $storage->getTableMapping()
                ->getTableNames();
            $db_schema = $this->container
                ->get('database')
                ->schema();
            foreach ($tables as $table) {
                $this->assertTrue($db_schema->tableExists($table), "The entity type table '{$table}' for the entity type '{$entity_type_id}' should exist.");
            }
        }
    }
    
    /**
     * Enables modules for this test.
     *
     * This method does not install modules fully. Services and hooks for the
     * module are available, but the install process is not performed.
     *
     * To install test modules outside of the testing environment, add
     * @code
     * $settings['extension_discovery_scan_tests'] = TRUE;
     * @endcode
     * to your settings.php.
     *
     * @param string[] $modules
     *   A list of modules to install. Dependencies are not resolved; i.e.,
     *   multiple modules have to be specified individually. The modules are only
     *   added to the active module list and loaded; i.e., their database schema
     *   is not installed. hook_install() is not invoked. A custom module weight
     *   is not applied.
     *
     * @throws \LogicException
     *   If any module in $modules is already enabled.
     * @throws \RuntimeException
     *   If a module is not enabled after enabling it.
     */
    protected function enableModules(array $modules) {
        // Perform an ExtensionDiscovery scan as this function may receive a
        // profile that is not the current profile, and we don't yet have a cached
        // way to receive inactive profile information.
        // @todo Remove as part of https://www.drupal.org/node/2186491
        $listing = new ExtensionDiscovery($this->root);
        $module_list = $listing->scan('module');
        // In ModuleHandlerTest we pass in a profile as if it were a module.
        $module_list += $listing->scan('profile');
        // Set the list of modules in the extension handler.
        $module_handler = $this->container
            ->get('module_handler');
        // Write directly to active storage to avoid early instantiation of
        // the event dispatcher which can prevent modules from registering events.
        $active_storage = $this->container
            ->get('config.storage');
        $extension_config = $active_storage->read('core.extension');
        foreach ($modules as $module) {
            if ($module_handler->moduleExists($module)) {
                continue;
            }
            $module_handler->addModule($module, $module_list[$module]->getPath());
            // Maintain the list of enabled modules in configuration.
            $extension_config['module'][$module] = 0;
        }
        $active_storage->write('core.extension', $extension_config);
        // Update the kernel to make their services available.
        $extensions = $module_handler->getModuleList();
        $this->container
            ->get('kernel')
            ->updateModules($extensions, $extensions);
        // Ensure isLoaded() is TRUE in order to make
        // \Drupal\Core\Theme\ThemeManagerInterface::render() work.
        // Note that the kernel has rebuilt the container; this $module_handler is
        // no longer the $module_handler instance from above.
        $module_handler = $this->container
            ->get('module_handler');
        $module_handler->reload();
        foreach ($modules as $module) {
            if (!$module_handler->moduleExists($module)) {
                throw new \RuntimeException("{$module} module is not installed after installing it.");
            }
        }
    }
    
    /**
     * Disables modules for this test.
     *
     * @param string[] $modules
     *   A list of modules to disable. Dependencies are not resolved; i.e.,
     *   multiple modules have to be specified with dependent modules first.
     *   Code of previously enabled modules is still loaded. The modules are only
     *   removed from the active module list.
     *
     * @throws \LogicException
     *   If any module in $modules is already disabled.
     * @throws \RuntimeException
     *   If a module is not disabled after disabling it.
     */
    protected function disableModules(array $modules) {
        // Unset the list of modules in the extension handler.
        $module_handler = $this->container
            ->get('module_handler');
        $module_filenames = $module_handler->getModuleList();
        $extension_config = $this->config('core.extension');
        foreach ($modules as $module) {
            if (!$module_handler->moduleExists($module)) {
                throw new \LogicException("{$module} module cannot be uninstalled because it is not installed.");
            }
            unset($module_filenames[$module]);
            $extension_config->clear('module.' . $module);
        }
        $extension_config->save();
        $module_handler->setModuleList($module_filenames);
        $module_handler->resetImplementations();
        // Update the kernel to remove their services.
        $this->container
            ->get('kernel')
            ->updateModules($module_filenames, $module_filenames);
        // Ensure isLoaded() is TRUE in order to make
        // \Drupal\Core\Theme\ThemeManagerInterface::render() work.
        // Note that the kernel has rebuilt the container; this $module_handler is
        // no longer the $module_handler instance from above.
        $module_handler = $this->container
            ->get('module_handler');
        $module_handler->reload();
        foreach ($modules as $module) {
            if ($module_handler->moduleExists($module)) {
                throw new \RuntimeException("{$module} module is not uninstalled after uninstalling it.");
            }
        }
    }
    
    /**
     * Renders a render array.
     *
     * @param array $elements
     *   The elements to render.
     *
     * @return string
     *   The rendered string output (typically HTML).
     */
    protected function render(array &$elements) {
        // \Drupal\Core\Render\BareHtmlPageRenderer::renderBarePage calls out to
        // system_page_attachments() directly.
        if (!\Drupal::moduleHandler()->moduleExists('system')) {
            throw new \Exception(__METHOD__ . ' requires system module to be installed.');
        }
        // Use the bare HTML page renderer to render our links.
        $renderer = $this->container
            ->get('bare_html_page_renderer');
        $response = $renderer->renderBarePage($elements, '', 'maintenance_page');
        // Glean the content from the response object.
        $content = $response->getContent();
        $this->setRawContent($content);
        return $content;
    }
    
    /**
     * Sets an in-memory Settings variable.
     *
     * @param string $name
     *   The name of the setting to set.
     * @param bool|string|int|array|null $value
     *   The value to set. Note that array values are replaced entirely; use
     *   \Drupal\Core\Site\Settings::get() to perform custom merges.
     */
    protected function setSetting($name, $value) {
        $settings = Settings::getInstance() ? Settings::getAll() : [];
        $settings[$name] = $value;
        new Settings($settings);
    }
    
    /**
     * Sets the install profile and rebuilds the container to update it.
     *
     * @param string $profile
     *   The install profile to set.
     */
    protected function setInstallProfile($profile) {
        $this->container
            ->get('config.factory')
            ->getEditable('core.extension')
            ->set('profile', $profile)
            ->save();
        // The installation profile is provided by a container parameter. Saving
        // the configuration doesn't automatically trigger invalidation
        $this->container
            ->get('kernel')
            ->rebuildContainer();
    }
    
    /**
     * Dumps the current state of the virtual filesystem to STDOUT.
     */
    protected function vfsDump() {
        vfsStream::inspect(new vfsStreamPrintVisitor());
    }
    
    /**
     * Returns the modules to install for this test.
     *
     * @param string $class
     *   The fully-qualified class name of this test.
     *
     * @return array
     */
    private static function getModulesToEnable($class) {
        $modules = [];
        while ($class) {
            if (property_exists($class, 'modules')) {
                // Only add the modules, if the $modules property was not inherited.
                $rp = new \ReflectionProperty($class, 'modules');
                if ($rp->class == $class) {
                    $modules[$class] = $class::$modules;
                }
            }
            $class = get_parent_class($class);
        }
        // Modules have been collected in reverse class hierarchy order; modules
        // defined by base classes should be sorted first. Then, merge the results
        // together.
        $modules = array_values(array_reverse($modules));
        return call_user_func_array('array_merge_recursive', $modules);
    }
    
    /**
     * Prevents serializing any properties.
     *
     * Kernel tests are run in a separate process. To do this PHPUnit creates a
     * script to run the test. If it fails, the test result object will contain a
     * stack trace which includes the test object. It will attempt to serialize
     * it. Returning an empty array prevents it from serializing anything it
     * should not.
     *
     * @return array
     *   An empty array.
     *
     * @see vendor/phpunit/phpunit/src/Util/PHP/Template/TestCaseMethod.tpl.dist
     */
    public function __sleep() : array {
        return [];
    }

}