def test_change(self, coll_vdirs):
        coll, vdirs = coll_vdirs
        event = Event.fromString(event_dt, calendar=cal1, locale=aux.locale)
        coll.new(event, cal1)
        event = list(coll.get_events_on(aday))[0]
        assert event.calendar == cal1

        coll.change_collection(event, cal2)
        events = list(coll.get_events_on(aday))
        assert len(events) == 1
        assert events[0].calendar == cal2
Add a density grid to the model
dataset/ETHPy150Open pimutils/khal/tests/khalendar_test.py/TestCollection.test_change--crossover with--dataset/ETHPy150Open hyperion-rt/hyperion/hyperion/model/model.py/Model.add_density_grid