def test_synchronousImplicitErrorChain(self):
        """
        If a first L{Deferred} with a L{Failure} result is returned from a
        callback on a second L{Deferred}, the first L{Deferred}'s result is
        converted to L{None} and no unhandled error is logged when it is
        garbage collected.
        """
        first = defer.fail(RuntimeError("First Deferred's Failure"))
        second = defer.Deferred()
        second.addCallback(lambda ign, first=first: first)
        second.callback(None)
        firstResult = []
        first.addCallback(firstResult.append)
        self.assertIsNone(firstResult[0])
        self.assertImmediateFailure(second, RuntimeError)

        If a first L{Deferred} with a L{Failure} result is returned from a
        callback on a second L{Deferred}, the first L{Deferred}'s result is
        converted to L{None} and no unhandled error is logged when it is
        garbage collected.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_defer.py