'When performing an update, the existing instance does not count
as a match against unique_for_date.'

def test_updated_instance_excluded_from_unique_for_date(self):

    data = {'slug': 'existing', 'published': '2000-01-01'}
    serializer = UniqueForDateSerializer(instance=self.instance, data=data)
    assert serializer.is_valid()
    assert (serializer.validated_data == {'slug': 'existing', 'published': datetime.date(2000, 1, 1)})
