bug.py

from twisted.internet.defer import Deferred
from twisted.trial.unittest import TestCase


class Race(TestCase):
    def test_thing(self):
        outer, inner = Deferred(), Deferred()

        def raiser(_):
            raise ValueError()

        inner.callback(1)
        outer.callback(2)
        outer.addCallback(lambda _: inner)
        inner.addCallback(raiser)

        return outer