def test_oldFlattenableError(self):
        result = Deferred()
        element = Element()
        element.docFactory = stan(result)

        request = FakeRequest()
        context = WovenContext()
        context.remember(request)

        accumulator = []
        finished = oldFlatten(element, context, accumulator.append, lambda ign: ign)
        result.addErrback(lambda err: err.trap(RuntimeError))
        finished = self.assertFailure(finished, RuntimeError)
        result.errback(RuntimeError("test error"))
        return finished
If the old flattener encounters an asynchronous Failure while
dataset/ETHPy150Open twisted/nevow/nevow/test/test_element.py/FlattenIntegrationTests.test_oldFlattenableError