def test_start(self):
        """
        L{ThreadPool.start} creates the minimum number of threads specified.
        """
        pool = threadpool.ThreadPool(0, 5)
        pool.start()
        self.addCleanup(pool.stop)
        self.assertEqual(len(pool.threads), 0)

        pool = threadpool.ThreadPool(3, 10)
        self.assertEqual(len(pool.threads), 0)
        pool.start()
        self.addCleanup(pool.stop)
        self.assertEqual(len(pool.threads), 3)

        L{ThreadPool.start} creates the minimum number of threads specified.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_threadpool.py