[afiori]

> * Say I have a test over some deterministic code, and I make a small change to that code. I'd like to be able to run that test before and after, and get a diff of where the computation was the same vs. where it was different.

There are many things I do not like about ocaml build ecosystem but the last time I looked into it this was the default structure of test; is was possible to assert stuff in unit test, but you were "forced" to output something and then promote it to valid output; the next time the unit test are run the build tool check for diffs and you can choose whether the new output is wrong of whether it should be promoted to correct output.

I found it extremely flexible, expecially if you make an API change that would require to update dozens/hundreds of tests