Basics of testing signals in Django

I'm new to testing in Django and I was wondering how to write tests for signals.

I went over the documentation but I couldn't find anything helpful.

Let's say a have a simple pre_save signal for Reservation model and I want to change some attribute before saving it to the database.

My code looks like this:

@receiver(pre_save, sender=Reservation)
def set_destination_type(sender, instance, *args, **kwargs):
    points = ['New York', 'Rome', 'Paris']
    if instance.destination in points:
        instance.international = True
    instance.international = False

How would I approach this? Do I just create a reservation and assert that correct value was set? Do I test this function in isolation? I really don't know how to start.

Thanks!