Added a test to ensure empty sessions are saved.

        # The session is accessed so "Vary: Cookie" should be set.

        self.assertEqual(response['Vary'], 'Cookie')

    def test_empty_session_saved(self):

        """"

        If a session is emptied of data but still has a key, it should still

        be updated.

        """

        request = RequestFactory().get('/')

        response = HttpResponse('Session test')

        middleware = SessionMiddleware()

        # Set a session key and some data.

        middleware.process_request(request)

        request.session['foo'] = 'bar'

        # Handle the response through the middleware.

        response = middleware.process_response(request, response)

        self.assertEqual(tuple(request.session.items()), (('foo', 'bar'),))

        # A cookie should be set, along with Vary: Cookie.

        self.assertIn(

            'Set-Cookie: sessionid=%s' % request.session.session_key,

            str(response.cookies)

        )

        self.assertEqual(response['Vary'], 'Cookie')

        # Empty the session data.

        del request.session['foo']

        # Handle the response through the middleware.

        response = HttpResponse('Session test')

        response = middleware.process_response(request, response)

        self.assertEqual(dict(request.session.values()), {})

        session = Session.objects.get(session_key=request.session.session_key)

        self.assertEqual(session.get_decoded(), {})

        # While the session is empty, it hasn't been flushed so a cookie should

        # still be set, along with Vary: Cookie.

        self.assertGreater(len(request.session.session_key), 8)

        self.assertIn(

            'Set-Cookie: sessionid=%s' % request.session.session_key,

            str(response.cookies)

        )

        self.assertEqual(response['Vary'], 'Cookie')

# Don't need DB flushing for these tests, so can use unittest.TestCase as base class

class CookieSessionTests(SessionTestsMixin, unittest.TestCase):