Allow custom cleanup functions in TestScheduler

[piratefsh]

🚀 Feature Proposal

Allow custom cleanup functions to be run by TestScheduler. Currently, TestScheduler only runs cleanup for jest snapshots (code here).

I would like a way to specify a custom cleanup function, or to have an expectation that a custom matcher can export it's own cleanup function.

Motivation

Custom matchers generate snapshots that can be obsolete once the corresponding test files have been removed. See related jest-image-snapshot issue here: americanexpress/jest-image-snapshot#59 (comment)

When working with a custom matcher e.g. jest-image-snapshot, there doesn't seem to be a way to run a cleanup function after all tests have finished running. Custom matchers may also save snapshot files with their own naming format, which may not correspond to jest-snapshot naming conventions,

Example

See motivation above ^

Pitch

A cleanup should run after all tests have been completed, which is known to TestScheduler. As far as I can see, that is the best place that this can happen -- happy to hear out and discuss alternative implementations!

[piratefsh]

Hey, bumping this -- any thoughts?

[rickhanlonii]

Hey @piratefsh, it makes sense to me on the surface - how do you recommend we expose hooking into it?

[piratefsh]

Hey @rickhanlonii, my initial thought is that custom matchers can export a cleanup function that can be called by TestScheduler after all tests are done running. This is what jest-snapshot currently does.

For the cleanup to work for snapshot-style matchers, cleanup is passed in as arguments the following:

• all known test files and snapshot files (via something called HasteFS it seems)
• a way to resolve test -> snapshot file (this can be implemented by the matcher since it is the one that generates the snaps)

If it cannot find a corresponding test for a snapshot file, it assumes that the snapshot file is no longer valid. This assumes that it's a one-to-one mapping between test and snapshot file though, so there is that limitation.

Also, when running a subset of tests, the cleanup function only affect the related files. I can imagine it to get confusing if I ran a single test suite and it ends up cleaning up old snapshot from unrelated tests.

What do you think? Happy to think this through further and to hear your thoughts.

[SimenB]

a way to resolve test -> snapshot file (this can be implemented by the matcher since it is the one that generates the snaps)

How does that play with #6143?

[piratefsh]

@SimenB Oh cool, didn't know about that PR! It should work with custom resolvers. Since the cleanup function will be implemented by the matcher itself, it should have the access to use its resolver. I don't forsee any conflict there. Did you have any thoughts or concerns?

I am also open to working on this!

[SimenB]

A PR with the changes you need would be awesome! No guarantee we'll merge, but often easier to discuss when there's some concrete code to look at 🙂

[markov00]

Hey there any news on this?

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