[Bug]: Document v8 code coverage options

[spenserblack]

Version

28.1.0

Steps to reproduce

1. Clone https://github.com/spenserblack/jest-v8-coverage-issue
2. yarn
3. yarn test-v8, see that coverage is <100%
4. yarn test-babel, see that coverage is 100%

Expected behavior

That coverage with the v8 provider would be 100%, because the default switch case is ignored via /* istanbul ignore next */

Actual behavior

/* istanbul ignore next */ seems to be ignored when using the v8 provider.

Additional context

No response

Environment

System:
    OS: Linux 5.4 Ubuntu 20.04.4 LTS (Focal Fossa)
    CPU: (2) x64 Intel(R) Xeon(R) CPU E5-1603 v3 @ 2.80GHz
  Binaries:
    Node: 16.15.0 - /usr/bin/node
    Yarn: 1.22.18 - ~/.yarn/bin/yarn
    npm: 8.3.2 - ~/.npm/bin/npm
  npmPackages:
    jest: ^28.1.0 => 28.1.0

[mrazauskas]

You should use /* c8 ignore next */ comment with v8. See https://github.com/bcoe/c8#ignoring-uncovered-lines-functions-and-blocks

[spenserblack]

Thanks for pointing that out! That was a simple mistake on my part 🤦
Closing.

[SimenB]

We should probably mention this in our docs

[spenserblack]

Would it be possible to make this more clear in the docs?
My mistake comes from starting with this stackoverflow answer, and viewing the linked documentation mentioning istanbul. A ctrl+f of that same documentation yielded no results of c8.

[SimenB]

wanna send a pr? 🙂

[mrazauskas]

Indeed. Would be really nice to have docs covering difference between babel / v8 coverage.

For the beginning, perhaps a note on ignore comments could be added next to collectcoverage? Or better next to coverageProvider?

[SimenB]

Both, I think. Or at least in coverageProvider, and link to that section from collectCoverage

[spenserblack]

wanna send a pr?

Just checking if that was addressed to me or @mrazauskas 🙂

[mrazauskas]

Just do it, if that is interesting for you (;

[spenserblack]

Sure, I could do that 🙂
I'm guessing this is the file to adjust?
https://github.com/facebook/jest/blob/3b0a975269a3b712d0235f67fbd072dd9cb867b2/docs/Configuration.md?plain=1#L225-L229

I'm a bit worried that a note on ignore comments would be too specific. Perhaps it might be best to just have permalinks istanbul and c8 docs (example)?

[SimenB]

It's non obvious v8 provider needs c8 comments, so I do think it makes sense there

[mrazauskas]

Not sure which place is the best. Might be we all have somewhat different picture in our minds. Just try putting it together and open a PR. It is easier to reason about a real thing.

A general sentence with links should be enough. By the way, this looks like some draft (last bullet) – #11188

[spenserblack]

Made PR #12836 😃

[github-actions]

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