Same. The moment my tests need to care about implementation details, is the moment I stop trying to mock/fake/stub/etc stuff and just test against the real thin

Same. The moment my tests need to care about implementation details, is the moment I stop trying to mock/fake/stub/etc stuff and just test against the real thing if possible. I don't want to worry about whether a library is correctly implementing the real behavior of the real thing. I can understand wanting to mock/fake/stub/whatever stuff that is outside of your control, like a third-party HTTP API where you can't just send real requests just for testing. But for the situation in the article, those tests just seem too fragile to me. And a lot of effort for the comparatively little confidence added by the test results.