jest-reporters: Use global coverage thresholds as high watermarks

[Zache]

Summary

When Istanbul generates the some reports (like html & lcov) it uses watermarks to to provide visual feedback with colors. The default watermarks are 50% and 80%. Which in the html reports means that coverage under 50% is red and coverage over 80% is green. But we have a coverage threshold of 100%, so using the report to find any file with coverage between 80% and 100% can be quite difficult as @nemoDreamer describes here: #6578.

My solution is to provide istanbul with watermarks where the high watermarks are set to the global coverage threshold of each coverage category (branches, functions, lines, and statements)

Test plan

I added unit tests for my use case and for not having any global coverage threshold and tested my changes using yarn link

[SimenB]

Thanks!

[codecov-io]

Codecov Report

Merging #9416 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #9416      +/-   ##
=========================================
+ Coverage   64.77%   64.8%   +0.02%     
=========================================
  Files         280     281       +1     
  Lines       11988   11998      +10     
  Branches     2957    2959       +2     
=========================================
+ Hits         7765    7775      +10     
  Misses       3591    3591              
  Partials      632     632

Impacted Files	Coverage Δ
packages/jest-reporters/src/coverage_reporter.ts	51.21% <ø> (ø)	⬆️
packages/jest-reporters/src/get_watermarks.ts	100% <100%> (ø)

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[SimenB]

Thank you!

[jeysal]

Thanks so much @Zache, I love smart ideas like this that link together existing functionality of tools! 🎉
I realize it's a bit late for a review, but just one question: Have you checked what happens if the threshold / high watermark is lower than the default 50% / low watermark? Just wanna make sure it doesn't cause weird behavior.

[Zache]

@jeysal Thank you for your kind feedback. And regarding your question I don't think that would be a problem, I guess you would have my original problem in reverse but nothing should break.

[jeysal]

Right so based on that it looks like the custom value wouldn't matter then, it'll be red below 50%/low and green above that.

[github-actions]

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