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Unit tests as documentation

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94 points thunderbong | 1 comments | 17 Oct 24 17:22 UTC | HN request time: 0.199s | source
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lucianbr ◴[17 Oct 24 18:16 UTC] No.41872163[source]▶
One - unit tests explain nothing. They show what the output should be for a given input, but not why, or how you get there. I'm surprised by the nonchalant claim that "unit tests explain code". Am I missing something about the meaning of the english word "explain"?

Two - so any input value outside of those in unit tests is undocumented / unspecified behavior? A documentation can contain an explanation in words, like what relation should hold between the inputs and outputs in all cases. Unit tests by their nature can only enumerate a finite number of cases.

This seems like such an obviously not great idea...

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1. danielovichdk ◴[17 Oct 24 19:32 UTC] No.41872973[source]▶
This is one of those thing that is "by philosophy", and I understand, i think, what you are saying.

I do think that tests should not explain the why, that would be leaking too much detail, but at the same time the why is somewhat the result of the test. A test is a documentation of a regression, not of how code it tests is implemented/why.

The finite number of cases is interesting. You can definitely run single tests with a high number of inputs which of course is still finite but perhaps closer to a possible way of ensuring validity.