As you noticed services are called through $this->container->get() or \Drupal::service() in Kernel and Functional tests. On the first glance it doesn’t matter - we receive a service in any case and tests work, but there are nuances. Let’s figure it out.
Kernel tests
The service container is available through the internal variable $this->container and class \Drupal in Kernel tests.
Class \Drupal (located in core/lib/Drupal.php) - is a static service container wrapper. It was created to get services in procedural code, for instance, in hooks. We can (and have to) use dependency injection in classes, but there is no other choice to get services in procedural code.
So we can use $this->container->get() and \Drupal::service() to load services both in Kernel tests. Usage of \Drupal in tests is considered as anti-pattern because it was created for procedural code, but not for object oriented programming.
Therefore, it is preferable to call services in Kernel tests via $this->container->get().
Functional tests
Example 1
Let’s look at examples of functional tests using $this->container and \Drupal service containers, in which we need to enable and use the book module inside the test:
namespace Drupal\Tests\example\Functional;
use Drupal\Tests\BrowserTestBase;
class ContainerFunctionalTest extends BrowserTestBase {
/**
* Test is failed since 'book.manager' doesn't exist in $this->container service container.
*/
public function testContainerFail() {
$this->container->get('module_installer')->install(['book']);
// Error is shown "Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: You have requested a non-existent service "book.manager"."
$all_books = $this->container->get('book.manager')->getAllBooks();
$this->assertEmpty($all_books);
}
/**
* Test is passed since 'book.manager' exists in \Drupal::service() service container.
*/
public function testDrupalPass() {
\Drupal::service('module_installer')->install(['book']);
$all_books = \Drupal::service('book.manager')->getAllBooks();
$this->assertEmpty($all_books);
}
The test testContainerFail(), which uses $this->container, fails because after enabling the “book” module the container $this->container isn’t updated. Test testDrupalPass() passes - \Drupal::service includes all services from the just enabled module.
We need to initialise service container once again using $this->rebuildContainer(); or $this->container = \Drupal::getContainer(); to make the test testContainerFail() pass.
public function testContainerPass() {
$this->container->get('module_installer')->install(['book']);
// Initialise the service container once again to pass the test.
$this->rebuildContainer();
$all_books = $this->container->get('book.manager')->getAllBooks();
$this->assertEmpty($all_books);
}
Example 2
Let’s consider another example where service container is used in the hook:
/**
* Implements hook_ENTITY_TYPE_load().
*/
function example_user_load(array $entities) {
// Service container is re-initialised during cache flush.
drupal_flush_all_caches();
\Drupal::service('state')->set('test', 'bar');
}
Pay attention that drupal_flush_all_caches() is used in the hook.
Also there are two Functional tests:
namespace Drupal\Tests\example\Functional;
use Drupal\Tests\BrowserTestBase;
/**
* Tests behaviour of service containers in Functional tests.
*/
class StateFunctionalTest extends BrowserTestBase {
protected $defaultTheme = 'stark';
/**
* {@inheritdoc}
*/
protected static $modules = [
'example',
];
/**
* Test is passed since the state returns the correct value.
*/
public function testDrupalStatePass() {
\Drupal::service('state')->set('test', 'foo');
$this->assertEquals('foo', \Drupal::service('state')->get('test'));
\Drupal::entityTypeManager()->getStorage('user')->load(1);
$this->assertEquals('bar', \Drupal::service('state')->get('test'));
}
/**
* Test fails since \Drupal and $this->container point to different instances of State service.
*/
public function testContainerStateFail() {
$this->container->get('state')->set('test', 'foo');
$this->assertEquals('foo', $this->container->get('state')->get('test'));
$this->container->get('entity_type.manager')->getStorage('user')->load(1);
$this->assertEquals('bar', $this->container->get('state')->get('test'));
}
}
First test testDrupalStatePass(), where \Drupal is used, passes successfully, but second test testContainerStateFail() fails since in the example_user_load() cache has been cleaned and service container was initialised again. Currently there are two different instances of the service container in \Drupal and $this->container. In order to pass test successfully, we need to update service container $this->container using $this->rebuildContainer(); or $this->container = \Drupal::getContainer(); as in the first example.
/**
* Test passes since $this->container is updated manually.
*/
public function testContainerStatePass() {
$this->container->get('state')->set('test', 'foo');
$this->assertEquals('foo', $this->container->get('state')->get('test'));
$this->container->get('entity_type.manager')->getStorage('user')->load(1);
$this->rebuildContainer();
$this->assertEquals('bar', $this->container->get('state')->get('test'));
}
It’s inconvenient to update the service container $this->container manually, isn’t it? Can be hard to understand that service containers \Drupal and $this->container out of sync during writing tests.
So, use \Drupal::service() in Functional tests to avoid incomprehensible situations.
It is quite strange that we should use $this->container->get() in Kernel tests and \Drupal::service() in Functional tests. You can follow ticket where this issue is being resolved. I hope we will use unified approach in Drupal 10.