Feature Request: Code Coverage

[mlrawlings]

It would be really nice to get coverage reports by using nyc:

nyc puppet-run plugin:mocha [...mocha options] ./path/to/*.test.js

nyc automatically instruments the code running in the node process (and any subprocesses), but the bundled code will not be instrumented.

Potential implementation

I've actually worked on a similar tool which also bundles code and runs it in the browser and reports back to the console. We implemented nyc support by:

1. Checking if the runner was started by nyc
2. Adding an instrument plugin to the bundler
3. Grabbing the window.__coverage__ variable which the instrumenting reports to and sending it back to the server

With puppet-run, 1 and 3 would remain conceptually the same, but as far as I can tell, Parcel doesn't have an instrumentation plugin. I'm also unsure if it's possible to conditionally apply plugins.

I think the better solution might be to instrument the code after it goes through parcel and rely on sourcemaps to get accurate code coverage. babel-plugin-istanbul supports passing an inputSourcemap so the sourcemaps output by Parcel could be passed along.

[andywer]

Hey @mlrawlings!

That's a fair feature request. I would propose a different approach though:

• Let's use puppeteer to capture the code coverage via the Chromium built-in coverage feature
• Use puppeteer-to-istanbul to convert the coverage data

Maybe you are in the mood for a little contribution? :)