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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: 0.255s | 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. lcall ◴[17 Oct 24 20:54 UTC] No.41873690[source]▶
At least sometimes, it really helps for a test to say WHY it is done that way. I had a case where I needed to change some existing code, and all the unit tests passed but one. The author was unavailable. It was very unclear whether I should change the test. I asked around. I was about to commit the changes to the code and test when someone came back from vacation and helpfully explained. I hope I added a useful comment.