Run mocha processes parallel from a Grunt task.

parallel-test-task.js

module.exports = function (grunt) {
	// collect the test files from our test folder
	// for example grunt.file.expand
	function getTests () {
		var tests = [
			{
				filePath: '/Users/Mate/Desktop/LoginTest.js',
				name: 'Login test'
			},
			{
				filePath: '/Users/Mate/Desktop/LogoutTest.js',
				name: 'Logout test'
			}
		];

		return tests;
	}

	// create and return a function which starts the mocha child process
	function createTestRunner (test) {
		var capabilites = {
			browserName: 'firefox'
		};

		// this function will be executed by async.parallel in the grunt task
		return function (callback) {
			acuireSession(capabilities, function (err, sessionId) {
				// start the Mocha process after we got the browser running
				// and inject the sessionId ad an environment variable
				grunt.util.spawn({
					cmd: 'mocha',
					args: [test.filePath, '-R', 'json'],
					opts: {
						env: _.extend({}, process.env, {
							sessionId: sessionId,
							testName: test.name
						})
					}
				}, function (err, res) {
					// do something with res.stdout
					// which will contain Mocha's json output
					callback(err, res.stdOut);
				});
			});
		}
	}

	// get a test session for a specific browser and os type
	// (this will start a new browser on the selenium node)
	function acuireSession (capabilities, callback) {
		request({
			uri: 'http://localhost:4444/wh/hub/session',
			method: 'POST',
			headers: { 'content-type' : 'application/json;charset=UTF-8' },
			body: {
				JSON.stringify({ desiredCapabilities: capabilities })
			}
		}, function (err, response) {
			callback(err, response.sessionId)
		});
	}

	// register our grunt task, named 'selenium'
	grunt.registerTask('selenium', function () {
		var done = this.async(),
			// this will contain the list of test definitions (path to file, name, etc)
			tests = getTests(),
			// this will contain an array of executable test functions
			testRunners = _.map(tests, createTestRunner);

		// start all the tests at the same time
		async.parallel(testRunners, function (err, results) {
			// do something with aggregated Mocha results
			_.each(results, function (result) {
				console.log(result.stats.passed, result.stats.failed);
			});

			// let Grunt know our task is finished
			done();
		});
	});
};