def test_derive(self):
duration = Duration()
duration.set_flight_attr = Mock()
takeoff_dt = A('FDR Takeoff Datetime',
value=datetime(1970, 1, 1, 0, 1, 0))
landing_dt = A('FDR Landing Datetime',
value=datetime(1970, 1, 1, 0, 2, 30))
duration.derive(takeoff_dt, landing_dt)
duration.set_flight_attr.assert_called_once_with(90)
