def createSystem(self):
        """
        Create and return a brand new L{MemoryIOSystem}.

        The L{MemoryIOSystem} knows how to open new tunnel devices.

        @return: The newly created I/O system object.
        @rtype: L{MemoryIOSystem}
        """
        system = MemoryIOSystem()
        system.registerSpecialDevice(Tunnel._DEVICE_NAME, Tunnel)
        return system

        Create and return a brand new L{MemoryIOSystem}.

        The L{MemoryIOSystem} knows how to open new tunnel devices.

        @return: The newly created I/O system object.
        @rtype: L{MemoryIOSystem}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/pair/test/test_tuntap.py