def test_suggestThreadPoolSize(self):
        """
        Try to change maximum number of threads.
        """
        reactor.suggestThreadPoolSize(34)
        self.assertEqual(reactor.threadpool.max, 34)
        reactor.suggestThreadPoolSize(4)
        self.assertEqual(reactor.threadpool.max, 4)

        Try to change maximum number of threads.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_threads.py