I don't think testing the product alone is good enough, because when you give it tests it has to pass it prioritizes passing them at the expense of everything else — including code quality. I've seen it pull in random variables, break semantic functions, etc.

Oh, no. I test. Each. and. Every. Step.

I use a test harness, and step through the code, look at debug logs, and abuse the code, as much as possible.

Kind of a pain, but I find unit tests are a bit of a "false hope" kind of thing: https://littlegreenviper.com/testing-harness-vs-unit/

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