def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def __init__(self, test, rx_index, tx_index, nh_addr):
        self._test = test
        self._rx_index = rx_index
        self._tx_index = tx_index
        self._nh_addr = ip_address(nh_addr)