'The L{Deferred} returned by L{task.deferLater} is errbacked if the
supplied function raises an exception.'

def test_errback(self):

    def callable():
        raise TestException()
    clock = task.Clock()
    d = task.deferLater(clock, 1, callable)
    clock.advance(1)
    return self.assertFailure(d, TestException)
