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addons.mozilla.org ♥s unit tests. Again.

AMO has had an on-again off-again relationship with unit tests. A little over a year ago we had a thousand unit tests that sort of, mostly, ran. The problem is, PHP unit testing just isn’t as good as it should be. CakePHP relies on SimpleTest, one of the main PHP test suites. It worked relatively well for a small number of tests, but as our suite grew, so did our troubles.

Our main issue was hitting a memory limit or the max execution time. We hit the limits often for a variety of reasons, some legitimate bugs, and some because we tried to hack around things to make the tests run. If we change the limits we affect the tests because they are running within the same environment. There wasn’t really a concept of fixtures then, although it looks like CakePHP has stepped up there. The simple test web runner was hard to use and the mock objects were sometimes a little too mocked and missing some attributes.

All in all it was a heroic effort to get that many tests, but we didn’t maintain it because they were so slow to write and difficult to run. Testing can be a pain to write, sure, but it shouldn’t be a burden like that. Enter Django’s testing suite (built on top of Python’s unittest). It has most of our complaints handled out of the box. It’s very well documented, considers a lot of aspects of testing, supports fixtures, a built-in client, etc. It’s a well thought out framework to build tests on.

We’re being more vigilant about requiring tests this time around, but they also aren’t as frustrating to write. When you write them they actually work and they stay working. Most of what you want is built in already. For example, I wrote the password reset form we needed on AMO in Django. With CakePHP and SimpleTest I’d have no idea how to test that the email was actually working. It’s apparently possible with a SimpleTest add-on and enough code that I have to scroll in my browser. With Django’s test suite the actual code was 5 lines, 3 of which were assertions:

def test_request_success(self):
                    {'email': self.user.email})

    eq_(len(mail.outbox), 1)
    assert mail.outbox[0].subject.find('Password reset') == 0
    assert mail.outbox[0].body.find('pwreset/%s' % self.uidb36) > 0

With the power of the new test suite we’re once again writing and maintaining our unit tests - currently at around 390 tests and increasing steadily. Plenty of people have written about why unit tests are important so I won’t belabor the point, but I will mention that it’s a great feeling to be able to commit something and be confident it hasn’t affected other parts of the site. It’s almost as good of a feeling when you write your code and a completely different test fails pointing out a case that you didn’t even consider but one that would soak up developer time trying to debug down the road.

Building on a foundation that takes testing seriously is great.

This is a static site. If you have any comments please start a thread in the fediverse and tag me or send an email.