How to use the nightwatch.bs_local function in nightwatch

if (isLocal) {
  if (isLocal && (!process.env.BS_USER || !process.env.BS_KEY)) {
    console.log(
      'Hey!\n',
      'You are missing credentials for Browserstack.\n',
      'If you are a contributor, this is normal, credentials are private. These tests must be run by a maintainer of vue-router',
      'If you are a maintainer, make sure to create your `.env` file with both `BS_USER` and `BS_KEY` variables!'
    )
    // fail if testing locally
    process.exit(process.env.CI ? 0 : 1)
  }

  let bsLocal
  const browserstack = require('browserstack-local')
  Nightwatch.bs_local = bsLocal = new browserstack.Local()
  bsLocal.start({ key: process.env.BS_KEY }, error => {
    if (error) throw error

    console.log('Connected. Now testing...')
    try {
      Nightwatch.cli(argv => {
        adaptArgv(argv)
        Nightwatch.CliRunner(argv)
          .setup(null, () => {
            // NOTE: I don't know when this is running or if it does
            // Code to stop browserstack local after end of parallel test
            bsLocal.stop(() => {
              server && server.close()
              process.exit(0)
            })
          })

#!/usr/bin/env node

var Nightwatch = require("nightwatch")
var browserstack = require("browserstack-local")
var bs_local

try {
  process.mainModule.filename = "./node_modules/nightwatch/bin/nightwatch"
  // Code to start browserstack local before start of test
  console.log("Connecting local")
  Nightwatch.bs_local = bs_local = new browserstack.Local()
  bs_local.start(
    {
      key: process.env.BROWSERSTACK_ACCESS_KEY
    },
    function(error) {
      if (error) throw error

      console.log("Connected. Now testing...")
      Nightwatch.cli(function(argv) {
        Nightwatch.CliRunner(argv)
          .setup(null, function() {
            // Code to stop browserstack local after end of parallel test
            bs_local.stop(function() {})
          })
          .runTests(function() {
            // Code to stop browserstack local after end of single test

const globals = require('./nightwatch.globals');

const cp = require('child_process');
const httpServer = require('http-server');

const browserstack = require('browserstack-local');
const nightwatch = require('nightwatch');
const chromedriver = require('chromedriver');

const server = httpServer.createServer(); // {root:'./'}
const configs = Object.keys(conf.test_settings);

let bsLocal = null;

if (~process.argv.indexOf('--bs') || process.env.NIGHTWATCH_BROWSERSTACK) {
    bsLocal = nightwatch.bs_local = new browserstack.Local;
}

beforeTests().then(doTests).then(afterTest).then(process.exit);

function beforeTests() {

    server.listen(globals.port, globals.host);

    return new Promise(res => {

        if (bsLocal) {
            bsLocal.start({}, err => {

                if (err) {
                    if (err.message.indexOf('another browserstack local')) {
                        console.log('re-using running bs-local instance');

#!/usr/bin/env node

var Nightwatch = require('nightwatch');
var browserstack = require('browserstack-local');
var bs_local;

try {

  process.mainModule.filename = "./node_modules/nightwatch/bin/nightwatch"
  // Code to start browserstack local before start of test
  console.log("Connecting local");
  Nightwatch.bs_local = bs_local = new browserstack.Local();
  bs_local.start({'key': process.env.BROWSERSTACK_ACCESS_KEY }, function(error) {
    if (error) throw error;

    console.log('Connected. Now testing...');
    Nightwatch.cli(function(argv) {
      Nightwatch.CliRunner(argv)
        .setup(null, function(){
          // Code to stop browserstack local after end of parallel test
          bs_local.stop(function(){});
        })
        .runTests(function(){
          // Code to stop browserstack local after end of single test
          bs_local.stop(function(){});
        });
    });
  });

e => {
    return [
      e.browser,
      e.browser_version,
      e.os,
      e.os_version
    ].join('_').replace(/\./g, '-').replace(/ /g, '_');
  }
);

try {
  process.mainModule.filename = './node_modules/nightwatch/bin/nightwatch';

  // Code to start browserstack local before start of test
  console.log('Connecting localhost to Browserstack...');
  Nightwatch.bs_local = bs_local = new browserstack.Local();
  bs_local.start({
    key: process.env.BROWSERSTACK_ACCESS_KEY,
    localIdentifier: ('wvtester19234' + process.env.BROWSERSTACK_USER).replace(/[^a-zA-Z0-9]/g, ''),
    force: 'true' // if you want to kill existing ports
  }, function(error) {
    if (error) throw new Error(error);
    console.log('Connected. Running tests...');
    console.log('Go to https://www.browserstack.com/automate to view tests in progress.');

    Nightwatch.cli(argv => {
      var envString = environment_names.join(',');
      argv.e = envString;
      argv.env = envString;
      Nightwatch.CliRunner(argv)
        .setup(null, () => {
          bs_local.stop(() => {

/*eslint no-console: "allow"*/

const gulp = require('gulp');
require('../gulpfile.js');
const webpack = require('webpack');
const compiler = webpack(require('../webpack.config.js'));
const WebpackDevServer = require('webpack-dev-server');
const Nightwatch = require('nightwatch');
const browserstack = require('browserstack-local');

const server = new WebpackDevServer(compiler, {
	contentBase: '../src/docs/',
	stats: 'errors-only',
});
const local = new browserstack.Local();
Nightwatch.bs_local = local;
const browserStackConfig = {
	key: process.env.BROWSERSTACK_ACCESS_KEY,
};

try {

	process.mainModule.filename = './node_modules/.bin/nightwatch'

	console.log('generate docs');
	gulp.start('docs-build', () => {

		console.log('start webpack server');
		server.listen(8080, 'localhost', err => {

			if (err) {
				console.log('webpack server start error');