CI vs. pre-commit

[chillenzer]

I noticed that we talk a bit about CI but not at all about pre-commit. They serve different purposes and not necessarily imply each other but for my personal work I rely significantly more on pre-commit than on CI (because whatever CI would be running is already ran by pre-commit). I'm aware that CI is probably the more important part, so we don't need to discuss that but should we add (at least a mentioning of) pre-commit somewhere?

[edbennett]

Yes, mentioning it is a good idea. Pre-commit itself discourages running the test suite in pre-commit, but other checks definitely are worth mentioning.

[chillenzer]

Really? Why? Where?

[edbennett]

• Yes
• Because pre-commit hooks should be fast and test suites are typically not fast enough
• Here

[chillenzer]

Well, I think it is a problem of defaults and software engineering skills. I think the default should be to have all tests running in pre-commit and have a (unit-) test suite that runs in very few seconds. The latter is the software engineering skill of keeping the unit tests small and to the point, i.e. finding minimal test cases that require very little resources (the book example in the lesson is a particularly bad example for that) and testing enough but not excessively. If despite all efforts, this becomes unacceptably large, then one should first define a subset of the tests that is fast enough to still run every time, find a mechanism to only run affected tests and only after both of the previous are not enough any more disable tests in pre-commit again. I'm confident that most of the people we teach won't hit that point with their software really.

[chillenzer]

Finally, it's personal preference that you could manually switch off on your machine if you don't like it.

[chillenzer]

Okay. After reading a bit more about this, the pre-commit maintainers seem to be pretty annoyed by this discussion by now. Mmmmhhh... it's probably something that is really dependent on the project size. But using TDD a lot, I usually run my test suite multiple times even before committing and it has saved me a lot of trouble when pre-commit still found a failing test.

[edbennett]

The pre-commit dev is rather opinionated, and this creates some QOL issues in some areas. (E.g. the repeated argument over whether it's reasonable to demand us to define our requirements in two separate places, one just for pre-commit.)

Personally I have yet to encounter a codebase with a non-trivial test suite that runs in a reasonable amount of time, so I don't think saying it's a skill issue is helpful.

[chillenzer]

Okay. That might be my lack of experience. Will report back in ten years. =)

[chillenzer]

PS: I said that it is a skill to keep them short but not that it is a lack of skill if it still gets out of hands at some point. That skill will only help you in pushing this boundary a little further which is all I advocated for. Again, I'm talking about the specific use case of our learners probably having relatively small projects (for starters).

[edbennett]

Many students on the CDT end up contributing to larger projects (e.g. HiRep, Bilby, ...) that will have large test suites.

And even if not, if possible I'd like to avoid a situation where a student adds more tests to their work and pushes up the runtime of the test suite such that

a. they think "oh no, I'm an awful programmer and a terrible person and don't deserve to be here", or
b. they remove tests to make the test suite faster and therefore "better"
c. they disable pre-commit altogether

(Also I'd be cautious about giving advice directly contradicted by the authors of a tool until learners have more experience in the area.)