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, nh, pmtu, table_id=0):
        self._test = test
        self.nh = nh
        self.pmtu = pmtu
        self.table_id = table_id