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
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
library that I've never really gotten a handle on. I
thought I could use this library here, and tried to mock
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
method, but just
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
self.lti needs to be set,
and it also needs to respond to a
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
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.