def test_persistence(self):
        """
        Threadpools can be pickled and unpickled, which should preserve the
        number of threads and other parameters.
        """
        pool = threadpool.ThreadPool(7, 20)

        self.assertEqual(pool.min, 7)
        self.assertEqual(pool.max, 20)

        # check that unpickled threadpool has same number of threads
        copy = pickle.loads(pickle.dumps(pool))

        self.assertEqual(copy.min, 7)
        self.assertEqual(copy.max, 20)

        Threadpools can be pickled and unpickled, which should preserve the
        number of threads and other parameters.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_threadpool.py