How to Mock Non-Standard Authentication in a Django View Test

Ideally when making automated tests, you don’t have to mock anything. You just test exactly what would be executed in production. Some scenarios make that a challenge, though. What if you’re testing a view that relies on an external authentication service, like an LTI server?

It’s probably possible to automate an LTI server to run alongside my tests, just like a test database. But that adds a lot of complexity without adding much value. Although that would make the test environment more similar to the production one, right now I just want to be able to detect regressions in my custom view.

I’m making a test for a view that uses LTIAuthMixin from the django-lti-provider library. If you look at LTIAuthMixin, you can see that all the authentication is handled in dispatch(), a method that’s called with each HTTP method of a view object (.get(), .post(), .put(), etc). Python has a mock library that I’ve never really gotten a handle on. I thought I could use this library here, and tried to mock out LTIAuthMixin’s dispatch() method. I was able to get my test to ignore LTI authentication, but I couldn’t figure out how to tell my mocked dispatch method to still return the necessary response data given a request with an authed user. So I kept thinking of alternatives, keeping in mind that all I cared about testing here is not even the view’s .get() method, but just .get_context_data().

Through a combination of Django’s RequestFactory and directly instantiating the view object, you can just alter its attributes as necessary. So I made a plan to not use Django’s test client, and just do something like this:

# LoggedInTestMixin just sets self.u to an authenticated user.

class MyLTILandingPageTest(LoggedInTestMixin, TestCase):
    def setUp(self):
        super(MyLTILandingPageTest, self).setUp()
        self.factory = RequestFactory()
        self.g = GraphFactory(title='Quiz graph',
                              needs_submit=True)
        self.submission = SubmissionFactory(
            graph=self.g, user=self.u, choice=3)

     def test_get(self):
        request = self.factory.get('/lti/landing/')
        request.user = self.u
        view = MyLTILandingPage()

        ctx = view.get_context_data()
        self.assertEqual(ctx.get('submissions').count(), 1)

The test above runs into a few errors. self.lti needs to be set, and it also needs to respond to a course_context() method call. This turned out to be sufficient:

class MockLTI(object):
    def course_context(self, request):
        return None

I also needed to attach the request object to the view I’ve instantiated, so it knows who the current user is. Here’s the completed test:

def test_get(self):
    request = self.factory.get('/lti/landing/')
    request.user = self.u
    view = MyLTILandingPage()
    view.lti = MockLTI()
    view.request = request

    ctx = view.get_context_data()
    self.assertEqual(ctx.get('submissions').count(), 1)
    submission = ctx.get('submissions').first()
    self.assertEqual(submission.user, self.u)
    self.assertEqual(submission.choice, 3)

Now my test confirms that this view’s context data contains a graph submission connected to the authenticated user. It doesn’t matter to get_context_data() that the user wasn’t actually authenticated with LTI.

So, if there’s a clearer, more idiomatic way to do this using Python’s standard mock library, maybe a way to override dispatch() using mock, I’d like see some examples.