replace foolscap.test.common.ShouldFailMixin.shouldFail with twisted.trial.unittest.TestCase.failUnlessFailure ?

[Zooko]

The foolscap shouldFail thing can require substrings, so maybe we need to use twisted.trial.unittest.TestCase.failUnlessSubstring too.

[Brian Warner]

I'm all for removing code, but we're currently compatible all the way back to Twisted-2.5.0, and I'd like to know what we're giving up to make a change like that.

In which version of Twisted did failUnlessFailure first appear?

(also, I think we probably have multiple versions of shouldFail, so we can probably consolidate them at the same time).

[Brian Warner]

I still think this is probably a good idea, but I'm no longer concerned about getting it into any particular release, including 0.6.5

[Brian Warner]

At this point, it should be replaced with e = yield self.assertFailure(f, *exceptionTypes), followed by an extra self.assertIn(substr, str(e)) when needed

And ideally we should avoid waiting for Deferreds at all, and use f = self.failureResultOf(d) which is synchronous.