"CeleryTask matching query does not exist" when running Django tests

I'm trying to test some part of a Django project. The test is:

class SearchTest(TestCase):
    def test_object_added(self):
            SomeSingleton().add_one_object_to_model()
            tmp = SomeModel.objects.latest('id')
            self.assertEqual(tmp.some_field,SOME_VALUE)

Here I'm calling some function to add somehow an object to a model. The creation model is related to some Celery task execution. The purpose of the test is to check a value of the field of the added model. So when an object is added to the model it becomes the latest by id.

I got this when I ran ./manage.py test some_app:

DoesNotExist: CeleryTask matching query does not exist.

I found this question here and tried to do the same thing. I changed 'id' in tmp = SomeModel.objects.latest('id') to all the possible variants: u'id', u'"id"' and even u"id" and u"'id'". I was still getting the same issue to the variants with single quotation sign type. But I got

FieldError: Invalid order_by arguments: [u'-"id"']

to the variants with both quotation sign types. It's alright, do we have any other ways to get the latest object of a model? I haven't found one that works. I tried to declare get_latest_by = "id" at class Meta but I got the same issue about query that doesn't exist.

I tried some Python ways (I still work with kind of a list, right?) like tmp = SomeModel.objects.all()[-1], SomeModel.objects.all()[len(SomeModel.objects.all())-1] and the issue was

AssertionError: Negative indexing is not supported.

Then I tried SomeModel.objects.all().reverse()[0] but was answered immediately:

IndexError: list index out of range

I'm frankly baffled. All of these ways work good when typed at ./manage.py shell so I can get the latest model but for some reason it doesn't happen when using ./manage.py test some_app. What is the right way to cope with it?