Idea: Completely reset all selectors in between test runs

[srmagura]

Context

I have a unit test that is checking selectFoo.recomputations() to confirm that recomputation only happens when it should. My test started failing due to a seemingly-unrelated change, and it turns out it was because I never called selectFoo.resetRecomputations() before my test.

I finally realized that memoized selectors are inherently stateful, and that my original test was almost certainly invalid and only passing because (weird reasons that I don't care enough to understand).

The Problem (if you can call it that)

I'd like each of my tests to start with a completely clean slate to prevent this issue from happening again. I don't see a good way to do this right now. It's not really practical to manually reset the cache & recomputations on every single one of my memoized selectors.

Idea

Add a top-level export to reselect like completelyResetAllOfMySelectors() which can be called in a beforeEach block. This could work by having reselect "remember" all of the selectors it has created so it can reset each one. Though I can also think of a different way to accomplish it.

Would this feature actually be useful to the community? I leaning towards "no" but I already wrote up the post so 🤷‍♀️

[markerikson]

Heh, I hate to rain on your parade twice in one day, but yeah, that's not really feasible here :)

For one thing it would require having some kind of magic global hook into every single selector that ever gets created. That seems complicated, and a lot of effort.

Memoized selectors are most definitely stateful. That's their whole purpose.

If you're testing just a selector by itself, then your best bet is to create a new instance of the selector in the test:

let selectSomeThing

beforeEach(() => {
  selectSomeThing = goMakeMeANewSelectorInstance()
})

Alternately, if you're using Jest, it clears out the module import cache for every separate test file. So, splitting up tests into separate files may be an option here.

[srmagura]

Hahahaha, no problem at all Mark! I realized as I was writing this that it would be a bit complex to implement and not overly useful. I think both of my feature proposals today should have started with "In an ideal world..."