Python / Django --是否有类似于Rails的assert_difference的断言？

Question

Rails有一个断言，在执行块后测试值的差异。来自这里

assert_difference 'Article.count', 1 do
  post :create, article: {...}
end  

此断言将执行post创建命令，并测试Article.count在执行块后是否增加了1。

Python或Django中是否有类似的断言？如果不是，最有效的实现是否只是存储数字，然后再得到它呢？

Answer 1

显式比隐式好

这在本质上也是一样的。

pre_count = Article.objects.count()

# Your Logic

post_count = Article.objects.count()

self.assertEqual(post_count-pre_count, 1)

或，对于额外的红宝石口味，

from django.utils.decorators import method_decorator
from contextlib import contextmanager

def ExtendedTestCase(TestCase):

    @method_decorator(context_manager)
    def assertDifference(self, func, diff, message=None):
        " A Context Manager that performs an assert. "
        old_value = func()
        yield # `with` statement runs here. Roughly equivalent to ruby's blocks
        new_value = func()
        self.assertEqual(new_value-old_value, diff, message)

def ArticleTestCase(ExtendedTestCase):

    def test_article_creation(self):
        " Test that new articles can be created "
        with self.assertDifference(Article.count, 1):
             self.client.post("/article/new/", {
                 "title": "My First Django Article",
                 "content": "Boring Technical Content",
             })