diff -u b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequiredValidator.php b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequiredValidator.php
--- b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequiredValidator.php
+++ b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequiredValidator.php
@@ -2,8 +2,12 @@
 
 namespace Drupal\user\Plugin\Validation\Constraint;
 
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Session\AccountProxyInterface;
 use Symfony\Component\Validator\ConstraintValidator;
 use Symfony\Component\Validator\Constraint;
+use Drupal\user\UserStorageInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Checks if the user's email address is provided if required.
@@ -12,7 +16,44 @@
  * and the user performing the edit has 'administer users' permission.
  * This allows users without email address to be edited and deleted.
  */
-class UserMailRequiredValidator extends ConstraintValidator {
+class UserMailRequiredValidator extends ConstraintValidator implements ContainerInjectionInterface {
+
+  /**
+   * User storage handler.
+   *
+   * @var \Drupal\user\UserStorageInterface
+   */
+  protected $userStorage;
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountProxyInterface
+   */
+  protected $currentUser;
+
+  /**
+   * Constructs the object.
+   *
+   * @param \Drupal\user\UserStorageInterface $user_storage
+   *   The user storage handler.
+   * @param \Drupal\Core\Session\AccountProxyInterface $current_user
+   *   The current user.
+   */
+  public function __construct(UserStorageInterface $user_storage, AccountProxyInterface $current_user) {
+    $this->userStorage = $user_storage;
+    $this->currentUser = $current_user;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity.manager')->getStorage('user'),
+      $container->get('current_user')
+    );
+  }
 
   /**
    * {@inheritdoc}
@@ -25,18 +66,16 @@
       return;
     }
 
-    $account = $items->getEntity();
     $existing_value = NULL;
 
     // Only validate for existing user.
     if (!$account->isNew() && $account->id()) {
-      $account_unchanged = \Drupal::entityTypeManager()
-        ->getStorage('user')
+      $account_unchanged = $this->userStorage
         ->loadUnchanged($account->id());
       $existing_value = $account_unchanged->getEmail();
     }
 
-    $required = !(!$existing_value && \Drupal::currentUser()->hasPermission('administer users'));
+    $required = !(!$existing_value && $this->currentUser->hasPermission('administer users'));
 
     if ($required && (!isset($items) || $items->isEmpty())) {
       $this->context->addViolation($constraint->message, ['@name' => $account->getFieldDefinition('mail')->getLabel()]);
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/user/tests/src/Unit/Plugin/Validation/Constraint/UserMailRequiredValidatorTest.php
@@ -0,0 +1,208 @@
+<?php
+
+namespace Drupal\Tests\user\Unit\Plugin\Validation\Constraint;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\user\Plugin\Validation\Constraint\UserMailRequired;
+use Drupal\user\Plugin\Validation\Constraint\UserMailRequiredValidator;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+
+/**
+ * @coversDefaultClass \Drupal\user\Plugin\Validation\Constraint\UserMailRequiredValidator
+ * @group user
+ */
+class UserMailRequiredValidatorTest extends UnitTestCase {
+
+  /**
+   * Creates a validator instance.
+   *
+   * @param bool $is_admin
+   *   Whether or not the current user is an administrator.
+   *
+   * @return \Drupal\user\Plugin\Validation\Constraint\UserMailRequiredValidator
+   *   The validator instance.
+   */
+  protected function createValidator($is_admin) {
+    // Setup mocks that don't need to change.
+    $unchanged_field = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $unchanged_field->expects($this->any())
+      ->method('getValue')
+      ->willReturn('unchanged-value');
+
+    $unchanged_account = $this->getMock('Drupal\user\UserInterface');
+    $unchanged_account->expects($this->any())
+      ->method('get')
+      ->willReturn($unchanged_field);
+    $user_storage = $this->getMock('Drupal\user\UserStorageInterface');
+    $user_storage->expects($this->any())
+      ->method('loadUnchanged')
+      ->willReturn($unchanged_account);
+    $current_user = $this->getMock('Drupal\Core\Session\AccountProxyInterface');
+    $current_user->expects($this->any())
+      ->method('id')
+      ->willReturn('current-user');
+    $current_user->expects($this->any())
+      ->method('hasPermission')
+      ->willReturn($is_admin);
+    return new UserMailRequiredValidator($user_storage, $current_user);
+  }
+
+  /**
+   * @covers ::validate
+   *
+   * @dataProvider providerTestValidate
+   */
+  public function testValidate($items, $expected_violation, $is_admin = FALSE) {
+    $constraint = new UserMailRequired();
+
+    // If a violation is expected, then the context's addViolation method will
+    // be called, otherwise it should not be called.
+    $context = $this->getMock(ExecutionContextInterface::class);
+
+    if ($expected_violation) {
+      $context->expects($this->once())
+        ->method('addViolation');
+    }
+    else {
+      $context->expects($this->never())
+        ->method('addViolation');
+    }
+
+    $validator = $this->createValidator($is_admin);
+    $validator->initialize($context);
+    $validator->validate($items, $constraint);
+  }
+
+  /**
+   * Data provider for ::testValidate().
+   */
+  public function providerTestValidate() {
+    $cases = [];
+
+    // Case 1: Empty user should be ignored.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn(NULL);
+    $cases[] = [$items, FALSE];
+
+    // Case 2: New users without an email should add a violation.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $account = $this->getMock('Drupal\user\UserInterface');
+    $account->expects($this->once())
+      ->method('isNew')
+      ->willReturn(TRUE);
+    $account->expects($this->never())
+      ->method('id');
+    $field_definition = $this->getMock('Drupal\Core\Field\FieldDefinitionInterface');
+    $field_definition->expects($this->once())
+      ->method('getLabel')
+      ->willReturn('label');
+    $account->expects($this->once())
+      ->method('getFieldDefinition')
+      ->willReturn($field_definition);
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn($account);
+    $items->expects($this->once())
+      ->method('isEmpty')
+      ->willReturn(TRUE);
+    $cases[] = [$items, TRUE];
+
+    // Case 3: Existing users without an email should add a violation.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $account = $this->getMock('Drupal\user\UserInterface');
+    $account->expects($this->once())
+      ->method('isNew')
+      ->willReturn(FALSE);
+    $account->expects($this->exactly(2))
+      ->method('id')
+      ->willReturn('current-user');
+    $field_definition = $this->getMock('Drupal\Core\Field\FieldDefinitionInterface');
+    $field_definition->expects($this->once())
+      ->method('getLabel')
+      ->willReturn('label');
+    $account->expects($this->once())
+      ->method('getFieldDefinition')
+      ->willReturn($field_definition);
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn($account);
+    $items->expects($this->once())
+      ->method('isEmpty')
+      ->willReturn(TRUE);
+    $cases[] = [$items, TRUE];
+
+    // Case 4: New users with an email should be ignored.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $account = $this->getMock('Drupal\user\UserInterface');
+    $account->expects($this->once())
+      ->method('isNew')
+      ->willReturn(TRUE);
+    $account->expects($this->never())
+      ->method('id');
+    $field_definition = $this->getMock('Drupal\Core\Field\FieldDefinitionInterface');
+    $field_definition->expects($this->once())
+      ->method('getLabel')
+      ->willReturn('label');
+    $account->expects($this->once())
+      ->method('getFieldDefinition')
+      ->willReturn($field_definition);
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn($account);
+    $items->expects($this->once())
+      ->method('isEmpty')
+      ->willReturn(FALSE);
+    $cases[] = [$items, FALSE];
+
+    // Case 5: Existing users with an email should be ignored.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $account = $this->getMock('Drupal\user\UserInterface');
+    $account->expects($this->once())
+      ->method('isNew')
+      ->willReturn(FALSE);
+    $account->expects($this->exactly(2))
+      ->method('id')
+      ->willReturn('current-user');
+    $field_definition = $this->getMock('Drupal\Core\Field\FieldDefinitionInterface');
+    $field_definition->expects($this->once())
+      ->method('getLabel')
+      ->willReturn('label');
+    $account->expects($this->once())
+      ->method('getFieldDefinition')
+      ->willReturn($field_definition);
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn($account);
+    $items->expects($this->once())
+      ->method('isEmpty')
+      ->willReturn(FALSE);
+    $cases[] = [$items, FALSE];
+
+    // Case 6: Existing users without an email should be ignored if the current
+    // user is an administrator.
+    $items = $this->getMock('Drupal\Core\Field\FieldItemListInterface');
+    $account = $this->getMock('Drupal\user\UserInterface');
+    $account->expects($this->once())
+      ->method('isNew')
+      ->willReturn(FALSE);
+    $account->expects($this->exactly(2))
+      ->method('id')
+      ->willReturn('current-user');
+    $field_definition = $this->getMock('Drupal\Core\Field\FieldDefinitionInterface');
+    $field_definition->expects($this->once())
+      ->method('getLabel')
+      ->willReturn('label');
+    $account->expects($this->once())
+      ->method('getFieldDefinition')
+      ->willReturn($field_definition);
+    $items->expects($this->once())
+      ->method('getEntity')
+      ->willReturn($account);
+    $cases[] = [$items, FALSE, TRUE];
+
+    return $cases;
+  }
+
+}