'Basic test that the method runs correctly with no ports'

def test__populate_ports_for_subnets_none(self):

    ports = []
    with mock.patch.object(directory, 'get_plugin') as get_p:
        get_p().get_networks.return_value = []
        self.db._populate_mtu_and_subnets_for_ports(mock.sentinel.context, ports)
    self.assertEqual([], ports)
