def test_callInThreadWithCallbackExceptionInCallback(self):
        """
        L{ThreadPool.callInThreadWithCallback} calls C{onResult} with a
        two-tuple of C{(False, failure)} where C{failure} represents the
        exception raised by the callable supplied.
        """
        class NewError(Exception):
            pass

        def raiseError():
            raise NewError()

        waiter = threading.Lock()
        waiter.acquire()

        results = []

        def onResult(success, result):
            waiter.release()
            results.append(success)
            results.append(result)

        tp = threadpool.ThreadPool(0, 1)
        tp.callInThreadWithCallback(onResult, raiseError)
        tp.start()

        try:
            self._waitForLock(waiter)
        finally:
            tp.stop()

        self.assertFalse(results[0])
        self.assertIsInstance(results[1], failure.Failure)
        self.assertTrue(issubclass(results[1].type, NewError))

        L{ThreadPool.callInThreadWithCallback} calls C{onResult} with a
        two-tuple of C{(False, failure)} where C{failure} represents the
        exception raised by the callable supplied.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_threadpool.py