SystemJS Istanbul Coverage Helper
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README.md

Provides a SystemJS translate hook for injecting Istanbul coverage reports into a SystemJS application.

In addition it comes with bundled support for the remap-istanbul project. This provides full coverage reports to the original sources be it ES6 or JSX etc, regardless of module format or SystemJS loader plugins used.

This is an experimental project, use at your own risk and support may be limited.

Using the coverage hook

The Istanbul coverage can be hooked into SystemJS through NodeJS via:

npm install systemjs-istanbul-hook
var systemIstanbul = require('systemjs-istanbul-hook');

systemIstanbul.hookSystemJS(SystemJS, function exclude(address) {
  // custom exclude function to skip coverage instrumentation for files
  return false;
});

There is an optional third parameter to the hook which is the coverageGlobal, by default __coverage__ is used.

Remapping coverage with source maps

Having hooked the loader, any code run through SystemJS.import will start populating the global __coverage__ object.

After running the code being tested, coverage can be remapped with source maps via:

var remappedCoverage = systemIstanbul.remapCoverage();
fs.writeFileSync('coverage.json', JSON.stringify(remappedCoverage, null, 2));

The full report against original sources can then be viewed via istanbul commandline operations:

cd folder/containing/coverage.json
istanbul report

and then viewing coverage/lcov-report/index.html.

Browser support

There are two ways to achieve coverage reports for browser code with this project:

1. Hook the builder, then create a bundle with coverage instrumentation

With this approach, we hook the builder via:

var Builder = require('systemjs-builder');
var systemIstanbul = require('systemjs-istanbul-hook');

var builder = new Builder('.');

// hook the builder loader before creating the bundle
systemIstanbul.hookSystemJS(builder.loader);

builder.bundle('test.js', 'out.js');

// having completed instrumentation, save the originalSources data
var originalSources = systemIstanbul.originalSources;

The rest is just wiring at this point - we then execute the bundle in the browser, and collect the __coverage__ global from the browser, before remapping back in the server:

var remappedCoverage = systemIstanbul.remapCoverage(coverageFromBrowser, originalSources);
fs.writeFileSync('coverage.json', JSON.stringify(remappedCoverage, null, 2));

2. Hook the builder, then use it to create a single-file precompilation server

This approach is identical to (1) above, except that instead of building a bundle, we can host a server that precompiles individual files:

var Builder = require('systemjs-builder');
var systemIstanbul = require('systemjs-istanbul-hook');

var builder = new Builder('.');

// hook the builder loader before creating the bundle
systemIstanbul.hookSystemJS(builder.loader);

builder.compile(requestedModule).then(function(output) {
  respondWith(output.source);
});

Collecting the __coverage__ from the browser and remapping it is then also identical to (1) above.

An example of this technique is included at https://github.com/guybedford/systemjs-istanbul/blob/master/test/compilation-server.js, which runs against the browser file https://github.com/guybedford/systemjs-istanbul/blob/master/test/test-browser.html.

License

MIT