unittest for django admin calling a celery task

admin.py

class PreparaLeilaoAdmin(admin.ModelAdmin):
    model = Leilao
    extra = 0
    can_delete = False
    form = LeilaoForm

    def save_model(self, request, obj, form, change):
        super(PreparaLeilaoAdmin, self).save_model(request, obj, form, change)
        
        arquivo = form.cleaned_data.get('arquivo')
        if arquivo:
            task_importar_arquivo.delay(arquivo)

test_admin.py

from mock import patch, Mock

from django.test import TestCase
from django.contrib.admin import AdminSite

from plugins.prepara_leilao.admin import PreparaLeilaoAdmin
from plugins.prepara_leilao.models import Leilao
from plugins.prepara_leilao.forms import LeilaoForm

class MockRequest(object):
    pass

class MockSuperUser(object):
    def has_perm(self, perm):
        return True

request = MockRequest()
request.user = MockSuperUser()

class PreparaLeilaoAdminTest(TestCase):

    def setUp(self):
        site = AdminSite()
        self.ma = PreparaLeilaoAdmin(Leilao, site)

    def test_model(self):
        self.assertEqual(self.ma.model, Leilao)

    def test_extra(self):
        self.assertEqual(self.ma.extra, 0)

    def test_can_delete(self):
        self.assertFalse(self.ma.can_delete)

    def test_form(self):
        self.assertEqual(self.ma.form, LeilaoForm)

    @patch('plugins.prepara_leilao.tasks.task_importar_arquivo.delay')
    def test_save_model(self, _delay):
        dummy_obj = Mock()
        dummy_form = Mock()
        dummy_form.cleaned_data = {
            'arquivo' : 'foo',
        }

        self.ma.save_model(request, dummy_obj, dummy_form, False)

        _delay.assert_called_once_with('foo')