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by stevekemp·2mo ago·view on hn ↗

I had a similar realization recently; I was writing a compiler so I implemented a "random" function as part of the runtime.

To avoid regression I have some simple code examples I compile and execute, and I compare their output to "known good" versions.

I reached a point where I wanted to write a "sort array" routine and my immediate thought was to generate an array of 50 random numbers, sort them, and print them. But of course that wouldn't give me predictable output for my test-driver.

In the end I decided I'd do that when run interactively, but for testing purposes I'd just sort the characters in a string "The quick brown fox .." and while it isn't super-convincing it's enough to let me see regressions in my sorting function and/or array indexing runtime code.

That's a bad example to use because it has very few repetitions (only the spaces I think?) and the key doesn't have different equivalent values so you can't test that you're order-preserving (or not).

But ideally sort is something you want to test with something like quickcheck/hypothesis, not gold tests (and I say that as probably the world's number 1 proponent of gold tests).