Coverage collection for Nightwatch.js browser tests

nightwatch-coverage.js

/**
 * Dependencies: js-yaml (for reading .istanbul.yml)
 *
 * Nightwatch coverage collection for browser testing, and writes the collected reports to the nightwatch
 * reports folder. These reports can then be used in conjunction with istanbul report to generate coverage
 * reports.
 */
var fs = require('fs');
var path = require('path');
var yaml = require('js-yaml');

var istanbulConfig = '.istanbul.yml';

module.exports = function(browser, done) {

    fs.access(istanbulConfig, fs.F_OK, function(err){

        var options = {};

        // If there's no errors then read the file
        if (err === null) {
            options = yaml.load(fs.readFileSync(istanbulConfig));
        }

        // Make sure there's an instrumentation object
        if (!options.instrumentation) {
            options.instrumentation = {};
        }

        // Get the coverage from the browser
        browser.execute(function(coverageVariable) {

            return window[coverageVariable];

        }, [ options.instrumentation.variable || '__coverage__' ], function(response){


            var filePath = path.join(
                'reports', //TODO: replace with nightwatch ouput_folder variable from config
                browser.currentTest.module || '',
                browser.currentTest.group || '',
                browser.currentTest.name || ''
            )
                .replace(/\s/gi, '-')       // normalise spaces
                .replace(/[\\\/]$/, '');    // remove trailing slash


            // Make sure something was returned - this will fail if browser.end() has been called
            if (response.status === 0 && response.value !== null) {

                // TODO: make folders if they don't exist
                fs.writeFileSync(filePath + '.json', JSON.stringify(response.value));

            }

            done();
        });

    });

};

FYI I created an npm module based on this: https://github.com/aberonni/nightwatch-coverage