Oni: Hook up code coverage to Jest tests

[bryphe]

We should hook up code-coverage via codecov to our Jest test framework.

[akinsho]

@bryphe I can take a look at this

[bryphe]

@Akin909 - that would be a huge help! 💯

PR #1533 would be a good reference point.

A couple of things we'd need to do:

• Run the Jest unit tests against the _instrumented bits_ - like we do here for the mocha unit tests:
  https://github.com/onivim/oni/blob/5e44c4419ccecefdbee0221bf5d23edb57ea52c4/build/script/travis-build.sh#L42

• For mocha, we needed a special hook to output the code coverage file. Jest might have an easier way, but this is how we hooked it for mocha:
  https://github.com/onivim/oni/blob/5e44c4419ccecefdbee0221bf5d23edb57ea52c4/browser/testCoverageReporter.js#L25

This outputs coverage date against the _built JavaScript files_.

• Lastly, we need to run the remap-istanbul to map the coverage back to the sourcemaps - that happens here:
  https://github.com/onivim/oni/blob/5e44c4419ccecefdbee0221bf5d23edb57ea52c4/package.json#L198

Hope that gives you some ideas! Thanks a lot for the help with this 👍

[akinsho]

A quick note this issue should be resolved once #2110 is merged, I've pointed jests coverage output dir to coverage/jest it outputs a coverage-final.json which I upload separately in the travis.yml codecov then does the magic of merging that report and the one for mocha into a single one

[akinsho]

closed by #2210