def test_uses_calc_time():
    primitive = TimeSinceLast()
    primitive_h = TimeSinceLast(unit="hours")
    datetimes = pd.Series([datetime(2015, 6, 6), datetime(2015, 6, 7)])
    answer = 86400.0
    answer_h = 24.0
    assert answer == primitive(datetimes, time=datetime(2015, 6, 8))
    assert answer_h == primitive_h(datetimes, time=datetime(2015, 6, 8))