'When passed a L{Deferred} which currently has a L{Failure} result (ie,
L{Deferred.addErrback} would cause the added errback to be called
before C{addErrback} returns), L{SynchronousTestCase.failureResultOf}
returns that L{Failure} if that L{Failure}\'s type is expected.'

def test_withExpectedFailureResult(self):

    self.assertIdentical(self.failure, self.failureResultOf(fail(self.failure), self.failure.type, KeyError))
