create @jest/core package

[SimenB]

Summary

We want to provide a programmatic API. A first step is to make jest-cli actually just deal with the CLI, and not everything else. We probably wanna make jest-core (or whatever it ends up being named) have a better API - for now it just expects a massaged argv object, which in theory can be constructed however you want.

We've discussed this briefly before, I just wanted to see how much work just the split was.

No hard feelings if it's not merged 🙂

I kept yargs and --init functionality in jest-cli

Test plan

Green CI?

[rubennorte]

I like the idea of doing this progressively, even if the boundary between jest-cli and jest-core isn't clear yet. I'd keep the README in jest-cli and have a temporary one in jest-core specifying it's internal and unstable to use directy.

[SimenB]

@rubennorte if you merge this, make sure to get publish access from @cpojer to jest-core: https://www.npmjs.com/package/jest-core (I like that it has 119 weekly downloads 😛)

[cpojer]

hell yeah

[SimenB]

Made it non-breaking (require('jest') and require('jest-cli') still returns the same thing they currently do), so gonna merge this if CI is happy

(@jest/core, fwiw)

[codecov-io]

Codecov Report

Merging #7696 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7696      +/-   ##
==========================================
- Coverage   58.32%   58.31%   -0.01%     
==========================================
  Files         164      163       -1     
  Lines        6047     6046       -1     
  Branches        5        5              
==========================================
- Hits         3527     3526       -1     
  Misses       2518     2518              
  Partials        2        2

Impacted Files	Coverage Δ
...st-core/src/getNoTestFoundRelatedToChangedFiles.js	0% <ø> (ø)
packages/jest-core/src/getNoTestFoundFailed.js	0% <ø> (ø)
packages/jest-core/src/TestWatcher.js	42.85% <ø> (ø)
packages/jest-cli/src/init/modify_package_json.js	100% <ø> (ø)
packages/jest-core/src/ReporterDispatcher.js	87.5% <ø> (ø)
packages/jest-core/src/plugins/quit.js	42.85% <ø> (ø)
packages/jest-core/src/TestNamePatternPrompt.js	44.44% <ø> (ø)
...t-core/src/plugins/update_snapshots_interactive.js	65.51% <ø> (ø)
packages/jest-cli/src/init/questions.js	100% <ø> (ø)
packages/jest-core/src/TestPathPatternPrompt.js	46.66% <ø> (ø)
... and 32 more

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[cpojer]

Holy shit, this PR is a dream come true. Amazing @SimenB, thank you!

[SimenB]

🎉 I've also split out @jest/reporters from jest-cli (would have been from @jest/core if this was merged first) and @jest/transform from jest-runtime. There's probably more stuff we can do, but at least this is a start 🙂

[github-actions]

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