def test_reserveOpensFileOnce(self):
        """
        Multiple acquisitions without releases open the reservation
        file exactly once.
        """
        self.assertEqual(len(self.reservedFileObjects), 0)

        for _ in range(10):
            self.reservedFD.reserve()
            self.assertEqual(len(self.reservedFileObjects), 1)
            self.assertFalse(self.reservedFileObjects[0].closed)

        Multiple acquisitions without releases open the reservation
        file exactly once.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_tcp.py