New helper method available to set up the "current_user" service in kernel tests

Setting up the current_user service in Kernel test is not completely trivial because user account 0 and 1 need to be created, along with the related schema. A new ::setUpCurrentUser() method is available on \Drupal\Tests\user\Traits\UserCreationTrait to do just that.

The new method creates a random user account and sets it as current user. Unless explicitly specified, a regular user account will be created and set as current, after creating user account 0 and 1. Additionally, the method will ensure that at least the anonymous user account exists regardless of the specified user ID.

This is also leveraged by Drupal\KernelTests\Core\Entity\EntityKernelTestBase, and also Drupal\Tests\node\Traits\NodeCreationTrait if no node author is specified and the current_user service has not been set up yet.

Note that the current_user service should be set up before any entity type schema relying on the user entity type is installed. See https://www.drupal.org/node/3036689 for details.

class MyTest1 extends KernelTestBase {

  use UserCreationTrait;

  public static $modules = [ 'system', 'user'];

  protected function setUp() {
    parent::setUp();
    // Sets up a regular authenticated user.
    $this->setUpCurrentUser();
    $this->installEntitySchema('my_entity_type');
  }

  public function testStuff1() {
    // ...
  }
}

class MyTest2 extends KernelTestBase {

  use UserCreationTrait;

  public static $modules = [ 'system', 'user'];

  protected function setUp() {
    parent::setUp();
    // Sets up an anonymous user.
    $this->setUpCurrentUser(['uid' => 0]);
    $this->installEntitySchema('my_entity_type');
  }

  public function testStuff2() {
    // ...
  }
}

class MyTest3 extends KernelTestBase {

  use UserCreationTrait;

  public static $modules = [ 'system', 'user'];

  protected function setUp() {
    parent::setUp();
    // Explicitly creates and sets up the root user.
    $this->setUpCurrentUser(['uid' => 1]);
    $this->installEntitySchema('my_entity_type');
  }

  public function testStuff3() {
    // ...
  }
}