[molf]

But ultimately it suggests this test; which only tests an empty loop?

  def test_empty_drc():
      drc = Mock(
          spec_set=DockerRegistryClient,
          get_repos=lambda: []
      )

      assert {} == get_repos_w_tags_drc(drc)

Maybe it's just a poor example to make the point. I personally think it's the wrong point to make. I would argue: don't mock anything _at all_ – unless you absolutely have to. And if you have to mock, by all means mock code you don't own, as far _down_ the stack as possible. And only mock your own code if it significantly reduces the amount of test code you have to write and maintain.

I would not write the test from the article in the way presented. I would capture the actual HTTP responses and replay those in my tests. It is a completely different approach.

[hynek]

Yes, because it's showing how the simplest-possible mock already gets ugly if you don't follow the advice. Making the example more complicated would dilute the point it's making.

The question of "when to mock" is very interesting and dear to my heart, but it's not the question this article is trying to answer.