Fixed #11400 -- Passed kwargs from AbstractUser.email_user() to send_mail()

Thanks Jug_ for suggestion, john_scott for the initial patch,
and Tim Graham for code review.

django/contrib/auth/tests/test_models.py

@@ -1,6 +1,7 @@
 from django.contrib.auth import get_user_model
-from django.contrib.auth.models import Group, User, UserManager
+from django.contrib.auth.models import AbstractUser, Group, User, UserManager
 from django.contrib.auth.tests.utils import skipIfCustomUser
+from django.core import mail
 from django.db.models.signals import post_save
 from django.test import TestCase
 from django.test.utils import override_settings
@@ -73,6 +74,29 @@ class UserManagerTestCase(TestCase):
                                   User.objects.create_user, username='')
 
 
+class AbstractUserTestCase(TestCase):
+    def test_email_user(self):
+        # valid send_mail parameters
+        kwargs = {
+            "fail_silently": False,
+            "auth_user": None,
+            "auth_password": None,
+            "connection": None,
+            "html_message": None,
+        }
+        abstract_user = AbstractUser(email='foo@bar.com')
+        abstract_user.email_user(subject="Subject here",
+            message="This is a message", from_email="from@domain.com", **kwargs)
+        # Test that one message has been sent.
+        self.assertEqual(len(mail.outbox), 1)
+        # Verify that test email contains the correct attributes:
+        message = mail.outbox[0]
+        self.assertEqual(message.subject, "Subject here")
+        self.assertEqual(message.body, "This is a message")
+        self.assertEqual(message.from_email, "from@domain.com")
+        self.assertEqual(message.to, [abstract_user.email])
+
+
 class IsActiveTestCase(TestCase):
     """
     Tests the behavior of the guaranteed is_active attribute