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Comment by AlphaSite | Hacker News Reader

My experience has been that TDD tends to do a poor job of testing complex systems with complex interactions. If any of the assumptions the tests are based on change (or are incorrect/brittle) then you will silently experience failures.

Integration testing is the more valuable side of testing imo but much harder and slower. Also not amiable to TDD in my experience.

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None of those tests will silently fail. That’s their point for existing. They complain when the code stops operating as the developer designed it to work.

Integration testing is valuable. It just isn’t scalable to the whole code base (because, as you said, it’s slow), that’s why macro tests should be targeted to the parts that can’t be micro tested (10-15%), leaving the bulk of the code to be tested with blazing fast micro tests. Agile Thoughts podcast goes over this during a series on the Testing Pramid, episodes 1 through 8. https://agilenoir.biz/series/agile-thoughts/

It’s not that the tests fail, so much as they become misleading. They still pass, but they pass because their assumptions are the programs assumptions, but their assumptions are wrong.

I don't think of TDD as being confined to unit tests and I was taught to test from outside in, meaning I'll have acceptance and integration testing as a matter of course.

It’s best to have both micro tests (TDD) and macro tests (Acceptance Tests, which if you write acceptance tests first, is referred to as ATDD). TDD refers to micro tests. ATDD is what you should say to communicate clearly what your doing. Saying TDD when you mean ATDD will cause confusion with those who have mature test automation practices. Macro versus micro are important distinctions as they need to be managed differently. Mix those two test inventories together actually causes damage as all your test infrastructure will be slow rather than having a micro test suite that’s faster and run more frequently. Check out Agile Thoughts episodes 1 through 8 for background on this. https://agilenoir.biz/series/agile-thoughts/

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