use a mock decorator for test methods that return Deferreds

[davidsarah]

Using the @mock.patch decorator for Trial test methods that return Deferreds does not work, because the patch will be undone when the method returns synchronously, not when the Deferred chain completes.

We should add a decorator that can be used instead to src/allmydata/test/common_util.py​. Something like:

def trialPatch(*patch_args, **patch_kwargs):
    patcher = mock.patch(*patch_args, **patch_kwargs)
    def decorator(f):
        def inner(*test_args, **test_kwargs):
            mock = patcher.__enter__()
            def cleanup(res):
                patcher.__exit__()
                return res
            test_args += (mock,)
            d = f(*test_args, **test_kwargs)
            d.addBoth(cleanup)
            return d
        return inner
    return decorator

This would require mock 0.6, I think. Thanks to ducki2p and voidspace for this code.

[zooko]

Please see #1395 for a working implementation of this and a discussion of whether we should actually maintain it in Tahoe-LAFS source tree or not.

[davidsarah]

The test added in #1149 could also benefit from this.

[davidsarah]

Is this useful? ​http://twistedmatrix.com/documents/10.1.0/api/twisted.trial.unittest.TestCase.html#patch

It's not as sophisticated as the mock library, but it might suffice for the cases we currently need, until we can depend on a version of mock that automatically handles deferreds.

[zooko]

Replying to davidsarah:

Is this useful? ​http://twistedmatrix.com/documents/10.1.0/api/twisted.trial.unittest.TestCase.html#patch

It's not as sophisticated as the mock library, but it might suffice for the cases we currently need, until we can depend on a version of mock that automatically handles deferreds.

Yeah, that looks potentially perfect. :-)

[zooko]

Everyone who finds this ticket, please use the Twisted "patch" utility: ​http://twistedmatrix.com/documents/10.1.0/api/twisted.trial.unittest.TestCase.html#patch for your unit tests.