def test_readFromEmpty(self):
        """
        Verify that reading from a file descriptor with no data does not raise
        an exception and does not result in the callback function being called.
        """
        l = []
        result = fdesc.readFromFD(self.r, l.append)
        self.assertEqual(l, [])
        self.assertIsNone(result)

        Verify that reading from a file descriptor with no data does not raise
        an exception and does not result in the callback function being called.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_fdesc.py