class ViewSetTest(TestCase):
    def test_view_set(self):
        factory = APIRequestFactory()
        view = CatViewSet.as_view()
        cat = Cat(name="bob")
        cat.save()

        request = factory.get(reverse('cat-detail', args=(cat.pk,)))
        response = view(request)

AttributeError: 'NoneType' object has no attributes 'items'

def test_client_view(self):
    response = APIClient().get(reverse('cat-detail', args=(cat.pk,)))
    self.assertEqual(response.status_code, 200)

response = view(request)

def test_view_set(self):
    request = APIRequestFactory().get("")
    cat_detail = CatViewSet.as_view({'get': 'retrieve'})
    cat = Cat.objects.create(name="bob")
    response = cat_detail(request, pk=cat.pk)
    self.assertEqual(response.status_code, 200)