[1.8.x] Added an import to docs/topics/testing/advanced.txt example.

Backport of 32b67b3fd1 from master

docs/topics/testing/advanced.txt

@@ -40,6 +40,8 @@ The following is a simple unit test using the request factory::
     from django.contrib.auth.models import AnonymousUser, User
     from django.test import TestCase, RequestFactory
 
+    from .views import my_view
+
     class SimpleTest(TestCase):
         def setUp(self):
             # Every test needs access to the request factory.