Ticket #13190: 13190_empty_auth_backends.diff.2

diff --git a/django/contrib/auth/__init__.py b/django/contrib/auth/__init__.py
index 169ae01..979f58d 100644
--- a/django/contrib/auth/__init__.py
+++ b/django/contrib/auth/__init__.py
@@ -39,6 +39,8 @@ def get_backends():
     backends = []
     for backend_path in settings.AUTHENTICATION_BACKENDS:
         backends.append(load_backend(backend_path))
+    if not backends:
+        raise ImproperlyConfigured('settings.AUTHENTICATION_BACKENDS is empty.')
     return backends
 
 def authenticate(**credentials):
diff --git a/django/contrib/auth/tests/__init__.py b/django/contrib/auth/tests/__init__.py
index a1d02b6..25d058e 100644
--- a/django/contrib/auth/tests/__init__.py
+++ b/django/contrib/auth/tests/__init__.py
@@ -1,4 +1,4 @@
-from django.contrib.auth.tests.auth_backends import BackendTest, RowlevelBackendTest, AnonymousUserBackendTest, NoAnonymousUserBackendTest
+from django.contrib.auth.tests.auth_backends import BackendTest, RowlevelBackendTest, AnonymousUserBackendTest, NoAnonymousUserBackendTest, NoBackendTest
 from django.contrib.auth.tests.basic import BASIC_TESTS
 from django.contrib.auth.tests.decorators import LoginRequiredTestCase
 from django.contrib.auth.tests.forms import UserCreationFormTest, AuthenticationFormTest, SetPasswordFormTest, PasswordChangeFormTest, UserChangeFormTest, PasswordResetFormTest
diff --git a/django/contrib/auth/tests/auth_backends.py b/django/contrib/auth/tests/auth_backends.py
index 8eaf2cb..9e6d338 100644
--- a/django/contrib/auth/tests/auth_backends.py
+++ b/django/contrib/auth/tests/auth_backends.py
@@ -1,6 +1,7 @@
 from django.conf import settings
 from django.contrib.auth.models import User, Group, Permission, AnonymousUser
 from django.contrib.contenttypes.models import ContentType
+from django.core.exceptions import ImproperlyConfigured
 from django.test import TestCase
 
 
@@ -245,3 +246,20 @@ class NoAnonymousUserBackendTest(TestCase):
 
     def test_get_all_permissions(self):
         self.assertEqual(self.user1.get_all_permissions(TestObj()), set())
+
+class NoBackendTest(TestCase):
+    """
+    Tests that an appropriate error is raised if no auth backends are provided.
+    """
+    backend = ()
+
+    def setUp(self):
+        self.curr_auth = settings.AUTHENTICATION_BACKENDS
+        settings.AUTHENTICATION_BACKENDS = self.backend
+        self.user = User.objects.create_user('test', 'test@example.com', 'test')
+
+    def tearDown(self):
+        settings.AUTHENTICATION_BACKENDS = self.curr_auth
+
+    def test_raises_exception(self):
+        self.assertRaises(ImproperlyConfigured, self.user.has_perm, ('perm', TestObj(),))