def test_callInThreadException(self):
        """
        L{ThreadPool.callInThread} logs exceptions raised by the callable it
        is passed.
        """
        class NewError(Exception):
            pass

        def raiseError():
            raise NewError()

        tp = threadpool.ThreadPool(0, 1)
        tp.callInThread(raiseError)
        tp.start()
        tp.stop()

        errors = self.flushLoggedErrors(NewError)
        self.assertEqual(len(errors), 1)

        L{ThreadPool.callInThread} logs exceptions raised by the callable it
        is passed.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_threadpool.py