'When the corresponding method on the provider of the interface raises
an exception, the ``Deferred`` fires with a ``Failure`` representing
that exception.'

def test_failure_result(self):

    failure = self.failureResultOf(self.async_spy.method(CannotAdd(), 1, 2), type(CannotAdd.EXCEPTION))
    self.assertEqual(CannotAdd.EXCEPTION, failure.value)
