* Ron Adam <ron3...@gmail.com> [2015-07-20 12:57:08 -0400]: > >It's "unsafe" because tests which: > > > >1) are using the assert_* methods of a mock, and > >2) where the programmer did a typo (assert_called() instead of > > assert_called_with() for example) > > > >do silently pass. > > And further down, you say... > > >Compare it with the behavior of a normal object - if you call a method > >which doesn't exist, it raises AttributeError. > > > >This isn't possible with Mock objects, as they are designed to support > >*any* call, and you can check the calls have happened after the fact. > > > And the docs say... > > """ > spec: This can be either a list of strings or an existing object (a class or > instance) that acts as the specification for the mock object. If you pass in > an object then a list of strings is formed by calling dir on the object > (excluding unsupported magic attributes and methods). Accessing any > attribute not in this list will raise an AttributeError. > """ > > So calling a method that doesn't exist on a mocked object will raise an > AttributeError if it is given a spec. > > But if you don't give it a spec, then a mispelling of *any* method will pass > silently. So it's not a problem limited to "assert" methods. > > It seems the obvious and best solution is to always use a spec.
I agree - I always use mocks with autospec/spec, and I recommend doing that - I actually plan to write a plugin for pylint to enforce this. Still mistyping the assert methods seems to be a common issue, since (according to some other mail) a couple of bugs in OpenStack were found this way. But yeah - if your code under test has a typo, and you don't use spec/autospec, you might not notice as well - though in my experience you *usually* do, since the returned mock object doesn't behave in the way you expect it to. But yeah - always using (auto)spec is probably the best solution. > >>> m.assert_me() > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > File > "/media/hda2/home/ra/Dev/python-dev/python3.5/cpython-master/Lib/unittest/mock.py", > line 583, in __getattr__ > raise AttributeError(name) > AttributeError: assert_me > > > Why is AttributeError raised here? Why are methods beginning with assert > special? (or "unsafe") Some things I can think of: - It's more likely that you use assert_called() instead of assert_called_with() accidentally than that you do a typo in your code under test. - If you do a typo in your code under test, a linter is more likely to find it than with mocks, because of their nature. - Other tests (even if they're manual ones) should probably discover the typo in your real code. The always-passing assert won't. Florian -- http://www.the-compiler.org | m...@the-compiler.org (Mail/XMPP) GPG: 916E B0C8 FD55 A072 | http://the-compiler.org/pubkey.asc I love long mails! | http://email.is-not-s.ms/
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