Что еще добавить в юнит тест для функции сортировки?

import json
...
test_data = {1: idx1, 2: idx2, ...}  # данные в нужном формате для передаче вьюхе
response = self.client.post(
    reverse("article:article_sorting"),
    json.dumps(test_data),
    content_type='application/json',
    follow=True
)

Traceback (most recent call last):
  File "/home/nurzhan/CA/static_pages/tests.py", line 120, in test_article_sorting
    self.assertEquals(first_article.idx, 2)
AssertionError: 0 != 2

def test_article_sorting(self):
        first_article = Article.objects.create(pk=150, idx=0, head='First')
        second_article = Article.objects.create(pk=160, idx=1, head='Second')
        third_article = Article.objects.create(pk=170, idx=2, head='Third')
        data = {150: 2, 160: 0, 170: 1}
        response = self.client.post(
            reverse("static_page:static_page_sorting"),
            data=json.dumps(data),
            content_type='application/json',
            follow=True
        )
        self.assertEqual(response.content, '{"saved": "OK"}')
        self.assertEqual(response.status_code, 200)
        self.assertEquals(first_article.idx, 2)  <-- ОШИБКА
        self.assertEquals(second_article.idx, 0)
        self.assertEquals(third_article.idx, 1)

first_article.refresh_from_db()
second_article.refresh_from_db()
third_article.refresh_from_db()
self.assertEquals(first_article.idx, 2)  <-- вот теперь норм должно быть
self.assertEquals(second_article.idx, 0)
self.assertEquals(third_article.idx, 1)

class Article(models.Model):
    image = models.ImageField(
        verbose_name='Изображение',
        upload_to='article/images/%Y/%m/%d/',
        blank=False,
    )

    def save(self, *args, **kwargs):
        try:
            article = Article.objects.get(id=self.id)
            if article.image != self.image:
                article.image.delete(save=False)
        except BaseException:
            pass
        super(Article, self).save(*args, **kwargs)

from django.core.files.uploadedfile import SimpleUploadedFile
        ***
        # Создаем изображение
        image = Image.new('RGB', (100, 100))
        file = tempfile.NamedTemporaryFile(suffix='.jpg')
        image.save(file)

        first_article = Article.objects.create(
                pk=150,
                idx=0,
                head='First',
                image=SimpleUploadedFile(
                        name='test.jpg',
                        content=open(file.name, 'rb').read(),
                        content_type='image/jpeg'
                )
        )

        second_article = Article.objects.create(
            pk=160,
            idx=1,
            head='Second',
            image=SimpleUploadedFile(
                name='test.jpg',
                content=open(file.name, 'rb').read(),
                content_type='image/jpeg'
            )
        )

        third_article = Article.objects.create(
            pk=170,
            idx=2,
            head='Third',        
            image=SimpleUploadedFile(
                name='test.jpg',
                content=open(file.name, 'rb').read(),
                content_type='image/jpeg'
            )
        )

        data = {150: 2, 160: 0, 170: 1}
        response = self.client.post(
            reverse("article:article_sorting"),
            data=json.dumps(data),
            content_type='application/json; charset= utf-8',
            follow=True
        )
        self.assertEqual(response.content, '{"saved": "OK"}')
        self.assertEqual(response.status_code, 200)

        first_article.refresh_from_db()
        print str(first_slide.idx)  <-- Возвращает 0, не обновилось. Должно быть 2 после обновления
        self.assertEquals(first_article.idx, 2)
        second_article.refresh_from_db()
        self.assertEquals(second_article.idx, 0)
        third_article.refresh_from_db()
        self.assertEquals(third_article.idx, 1)

Traceback (most recent call last):
  File "/home/nurzhan/CA/article/tests.py", line 176, in test_article_sorting
    self.assertEquals(first_article.idx, 2)
AssertionError: 0 != 2