diff --git a/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php b/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
index 552e56c..4ee9df2 100644
--- a/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
@@ -45,7 +45,7 @@ class UserRegistrationResource extends ResourceBase {
   protected $currentUser;
 
   /**
-   * Constructs a new RestPermissions instance.
+   * Constructs a new UserRegistrationResource instance.
    *
    * @param array $configuration
    *   A configuration array containing information about the plugin instance.
diff --git a/core/modules/rest/src/Tests/RegisterUserTest.php b/core/modules/rest/src/Tests/RegisterUserTest.php
index 09ccdf2..a5e2d58 100644
--- a/core/modules/rest/src/Tests/RegisterUserTest.php
+++ b/core/modules/rest/src/Tests/RegisterUserTest.php
@@ -25,16 +25,16 @@ class RegisterUserTest extends RESTTestBase {
   public static $modules = ['hal'];
 
   /**
-   * Enables user registration specific REST API configuration and authenticate.
+   * {@inheritdoc}
    */
-  protected function enableUserRegistrationConfiguration() {
+  public function setUp() {
+    parent::setUp();
     // Enabling services for the user registration and GET the new user entity
     // created.
     $config = $this->config('rest.settings');
     $settings = [];
     $resources = [
       ['type' => 'rest_user_registration', 'method' => 'POST'],
-      ['type' => 'entity:user', 'method' => 'GET']
     ];
     $format = 'hal_json';
     $auth = $this->defaultAuth;
@@ -50,7 +50,6 @@ protected function enableUserRegistrationConfiguration() {
     Role::load(RoleInterface::ANONYMOUS_ID)
       ->grantPermission('restful post rest_user_registration')
       ->save();
-
   }
 
   /**
@@ -58,7 +57,6 @@ protected function enableUserRegistrationConfiguration() {
    */
   protected function testRegisterUser() {
 
-    $this->enableUserRegistrationConfiguration();
     // New user info to be serialized.
     $data = [
       "_links" =>
@@ -77,7 +75,7 @@ protected function testRegisterUser() {
       ],
       "mail" => [
         [
-          "value" => "druplicon@superpoweredbydrupal.com"
+          "value" => "druplicon@example.com"
         ]
       ],
       "pass" => [
@@ -88,7 +86,7 @@ protected function testRegisterUser() {
     ];
 
     // Create a JSON version for the user entity we want to create.
-    $serialized = \Drupal::service('serializer')->serialize($data, 'hal_json');
+    $serialized = $this->container->get('serializer')->serialize($data, 'hal_json');
 
     // Post to the REST service to register the user.
     $this->httpRequest('entity/user/register', 'POST', $serialized, 'application/hal+json');
@@ -99,7 +97,8 @@ protected function testRegisterUser() {
     $id = end($url_parts);
     $this->assertHeader('Location', $GLOBALS['base_url'] . '/user/' . $id);
 
-    $this->assertTrue((bool) \Drupal::entityQuery('user')
+    $this->assertTrue((bool) $this->container->get('entity.query')
+      ->get('user')
       ->condition('name', 'Druplicon')
       ->range(0, 1)
       ->count()
diff --git a/core/modules/rest/tests/src/Unit/UserRegistrationResourceTest.php b/core/modules/rest/tests/src/Unit/UserRegistrationResourceTest.php
index c3f3f2c..778b534 100644
--- a/core/modules/rest/tests/src/Unit/UserRegistrationResourceTest.php
+++ b/core/modules/rest/tests/src/Unit/UserRegistrationResourceTest.php
@@ -7,41 +7,82 @@
 
 namespace Drupal\Tests\rest\Unit;
 
+use Drupal\Core\Config\ImmutableConfig;
+use Drupal\Core\Field\FieldItemList;
+use Drupal\Core\Session\AccountInterface;
 use Drupal\rest\Plugin\rest\resource\UserRegistrationResource;
 use Drupal\Tests\UnitTestCase;
+use Drupal\user\Entity\User;
+use Psr\Log\LoggerInterface;
+use Drupal\Core\Entity\EntityConstraintViolationList;
+use Symfony\Component\Validator\ConstraintViolationInterface;
 
 /**
  * Only administrators can create user accounts.
  */
-define('USER_REGISTER_ADMINISTRATORS_ONLY', 'admin_only');
+if (!defined('USER_REGISTER_ADMINISTRATORS_ONLY')) {
+  define('USER_REGISTER_ADMINISTRATORS_ONLY', 'admin_only');
+}
 
 /**
  * Visitors can create their own accounts.
  */
-define('USER_REGISTER_VISITORS', 'visitors');
+if (!defined('USER_REGISTER_VISITORS')) {
+  define('USER_REGISTER_VISITORS', 'visitors');
+}
 
 /**
  * Visitors can create accounts, but they don't become active without
  * administrative approval.
  */
-define('USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL', 'visitors_admin_approval');
-
+if (!defined('USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL')) {
+  define('USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL', 'visitors_admin_approval');
+}
 
 /**
  * Tests User Registration REST resource.
  *
+ * @coversDefaultClass \Drupal\Tests\rest\Unit\UserRegistrationResourceTest
  * @group rest
  */
 class UserRegistrationResourceTest extends UnitTestCase {
 
   const ERROR_MESSAGE = "Unprocessable Entity: validation failed.\nproperty_path: message\nproperty_path_2: message_2\n";
 
+  /**
+   * Class to be tested.
+   *
+   * @var \Drupal\rest\Plugin\rest\resource\UserRegistrationResource
+   */
   protected $testClass;
+
+  /**
+   * A reflection of self::$testClass.
+   *
+   * @var \ReflectionClass
+   */
   protected $reflection;
+
+  /**
+   * A user settings config instance.
+   *
+   * @var \Drupal\Core\Config\ImmutableConfig|\PHPUnit_Framework_MockObject_MockObject
+   */
   protected $userSettings;
+
+  /**
+   * Logger service.
+   *
+   * @var \Psr\Log\LoggerInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
   protected $logger;
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
   protected $currentUser;
-  protected $renderer;
 
   /**
    * {@inheritdoc}
@@ -49,14 +90,14 @@ class UserRegistrationResourceTest extends UnitTestCase {
   protected function setUp() {
     parent::setUp();
 
-    $this->logger = $this->getMock('Psr\Log\LoggerInterface');
+    $this->logger = $this->getMock(LoggerInterface::class);
 
-    $this->userSettings = $this->getMockBuilder('Drupal\Core\Config\ImmutableConfig')
+    $this->userSettings = $this->getMockBuilder(ImmutableConfig::class)
       ->setMethods(['get'])
       ->disableOriginalConstructor()
       ->getMock();
 
-    $this->currentUser = $this->getMockBuilder('Drupal\Core\Session\AccountInterface')
+    $this->currentUser = $this->getMockBuilder(AccountInterface::class)
       ->disableOriginalConstructor()
       ->getMock();
 
@@ -65,6 +106,14 @@ protected function setUp() {
 
   }
 
+  /**
+   * Helper method to set a protected method as accessible.
+   *
+   * @param string $method
+   *   The protected method.
+   *
+   * @return \ReflectionMethod
+   */
   public function getProtectedMethod($method) {
     $method = $this->reflection->getMethod($method);
     $method->setAccessible(TRUE);
@@ -72,9 +121,11 @@ public function getProtectedMethod($method) {
     return $method;
   }
 
+  /**
+   * Tests that the user entity does not violate any validation constraints.
+   */
   public function testValidate() {
-
-    $violations = $this->getMockBuilder('Drupal\Core\Entity\EntityConstraintViolationList')
+    $violations = $this->getMockBuilder(EntityConstraintViolationList::class)
       ->setMethods(['filterByFieldAccess'])
       ->disableOriginalConstructor()
       ->getMock();
@@ -83,14 +134,16 @@ public function testValidate() {
       ->method('filterByFieldAccess')
       ->will($this->returnValue(array()));
 
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
+
     $entity->expects($this->once())
       ->method('validate')
       ->will($this->returnValue($violations));
 
     $method = $this->getProtectedMethod('validate');
+
     // No exception is thrown.
     $method->invokeArgs($this->testClass, array($entity));
   }
@@ -100,25 +153,31 @@ public function testValidate() {
    * @expectedException UserRegistrationResourceTest::ERROR_MESSAGE
    */
   public function testFailedValidate() {
-    $violation1 = $this->getMock('Symfony\Component\Validator\ConstraintViolationInterface');
+    $violation1 = $this->getMock(ConstraintViolationInterface::class);
+
     $violation1->expects($this->once())
       ->method('getPropertyPath')
       ->will($this->returnValue('property_path'));
+
     $violation1->expects($this->once())
       ->method('getMessage')
       ->will($this->returnValue('message'));
-    $violation2 = $this->getMock('Symfony\Component\Validator\ConstraintViolationInterface');
+
+    $violation2 = $this->getMock(ConstraintViolationInterface::class);
+
     $violation2->expects($this->once())
       ->method('getPropertyPath')
       ->will($this->returnValue('property_path_2'));
+
     $violation2->expects($this->once())
       ->method('getMessage')
       ->will($this->returnValue('message_2'));
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
 
-    $violations = $this->getMockBuilder('Drupal\Core\Entity\EntityConstraintViolationList')
+    $violations = $this->getMockBuilder(EntityConstraintViolationList::class)
       ->setConstructorArgs([$entity, [$violation1, $violation2]])
       ->setMethods(['filterByFieldAccess'])
       ->getMock();
@@ -149,7 +208,7 @@ public function testEmptyPost() {
    * @expectedExceptionMessage Only new user accounts can be registered.
    */
   public function testExistedEntityPost() {
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
 
@@ -174,7 +233,7 @@ public function testRegistrationAdminOnlyPost() {
       ->will($this->returnValue(USER_REGISTER_ADMINISTRATORS_ONLY));
 
     $this->testClass = new UserRegistrationResource([], 'plugin_id', '', [], $this->logger, $this->userSettings, $this->currentUser);
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
 
@@ -195,9 +254,11 @@ public function testRegistrationAnonymousOnlyPost() {
       ->will($this->returnValue(FALSE));
 
     $this->testClass = new UserRegistrationResource([], 'plugin_id', '', [], $this->logger, $this->userSettings, $this->currentUser);
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
+
     $entity->expects($this->once())
       ->method('isNew')
       ->will($this->returnValue(TRUE));
@@ -215,16 +276,16 @@ public function testFieldAccessValidation() {
       ->will($this->returnValue(TRUE));
 
     $this->testClass = new UserRegistrationResource([], 'plugin_id', '', [], $this->logger, $this->userSettings, $this->currentUser);
-    $entity = $this->getMockBuilder('Drupal\user\Entity\User')
+
+    $entity = $this->getMockBuilder(User::class)
       ->disableOriginalConstructor()
       ->getMock();
 
-
     $entity->expects($this->once())
       ->method('isNew')
       ->will($this->returnValue(TRUE));
 
-    $field = $this->getMockBuilder('\Drupal\Core\Field\FieldItemList')
+    $field = $this->getMockBuilder(FieldItemList::class)
       ->setMethods(['access'])
       ->disableOriginalConstructor()
       ->getMock();