Coverage with Istanbul

I’m currently implementing coverage reporting with Istanbul and have coverage being written on a per-test basis, using a custom command.

Is there a way to hook a function into a global afterEach hook that will run with the same browser context as the test ran with, so it would have access to the same window object in the browser (to access the coverage variable)?

Are there any plans on adding coverage reporting into Nightwatch directly?

[munkyjunky]

@KBPratap I did manage to get it working, but it’s a bit of a faff to get working.

First you need to have a version of your website with instrumented code. You then need to run nightwatch against this instrumented version of your site, and before calling .end() in your tests you need to get the coverage information out of the window and write it to a file. I did this by creating a custom command, .finish, which does this, then calls .end, and stores coverage information into a data store.

In the global after in nightwatch I then write out reports to the file system from the store of data.

This isn’t a great method, but works for me. It has some limitations though, as if you get a full page load at any point in your test then you lose coverage information from the previous page. This wasn’t an issue for my project, but may be for you.

I haven’t been working with nightwatch in any projects recently so can’t say if there’s a better way of doing it, bit this worked for me.

var fs = require('fs');
var store = require('path/to/coverage/store');
var yaml = require('yaml-js');

var config = '.istanbul.yml';

/**
 * Wrapper around browser.end, which gives us chance to write coverage details before
 * the browser session is closed without having to manually do it in each test.
 *
 * @param callback {function}
 * @returns {exports}
 */
exports.command = function(callback) {

	var browser = this;

	fs.access(config, fs.R_OK, function(err) {

		var options = err ? {} : yaml.load(fs.readFileSync(config));

		// 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){

			// Make sure something was returned - this will fail if browser.end() has been called
			if (response.status === 0 && response.value !== null) {
				store.addReport({
					name: browser.currentTest.module + '/' + browser.currentTest.name.toLowerCase().replace(/\W/gi,'-').replace(/\-+/g, '-'),
					data: response.value
				});
			}

			// End the browser session
			browser.end(callback);

		});

	});

	return this;

};

[aberonni]

FWIW I setup an example repo that does something similar to what is illustrated above https://github.com/aberonni/nightwatch-test-coverage-example