How to use the appium-chromedriver.EVENT_CHANGED function in appium-chromedriver

async.eachSeries(Object.keys(this.sessionChromedrivers), function (context, cb) {
    logger.debug("Stopping chromedriver for context " + context);
    // stop listening for the stopped state event
    this.sessionChromedrivers[context].removeAllListeners(Chromedriver.EVENT_CHANGED);
    this.sessionChromedrivers[context].stop().nodeify(function (err) {
      if (err) logger.warn("Error stopping Chromedriver: " + err.message);
      // chromedriver isn't valid anymore, so remove it from context list
      delete this.sessionChromedrivers[context];
      cb();
    }.bind(this));
  }.bind(this), function (err) {
    // if one of these fails, go back to last proxy state and error out

ChromeAndroid.prototype.stop = function (cb) {
  // stop listening for the stopped state event
  this.chromedriver.removeAllListeners(Chromedriver.EVENT_CHANGED);
  // now we can handle the stop on our own
  this.chromedriver.stop().nodeify(function (err) {
    if (err) logger.warn("Error stopping Chromedriver: " + err.message);
    this.onChromedriverStop(cb);
  }.bind(this));
};

const knownPackages = [
    'org.chromium.chrome.shell',
    'com.android.chrome',
    'com.chrome.beta',
    'org.chromium.chrome',
    'org.chromium.webview_shell',
  ];

  if (_.includes(knownPackages, this.opts.appPackage)) {
    opts.chromeBundleId = this.opts.appPackage;
  } else {
    opts.chromeAndroidActivity = this.opts.appActivity;
  }
  this.chromedriver = await this.setupNewChromedriver(opts, this.adb.curDeviceId, this.adb);
  this.chromedriver.on(Chromedriver.EVENT_CHANGED, (msg) => {
    if (msg.state === Chromedriver.STATE_STOPPED) {
      this.onChromedriverStop(CHROMIUM_WIN);
    }
  });

  // Now that we have a Chrome session, we ensure that the context is
  // appropriately set and that this chromedriver is added to the list
  // of session chromedrivers so we can switch back and forth
  this.curContext = CHROMIUM_WIN;
  this.sessionChromedrivers[CHROMIUM_WIN] = this.chromedriver;
  this.proxyReqRes = this.chromedriver.proxyReq.bind(this.chromedriver);
  this.jwpProxyActive = true;

  if (this.shouldDismissChromeWelcome()) {
    // dismiss Chrome welcome dialog
    await this.dismissChromeWelcome();

helpers.stopChromedriverProxies = async function stopChromedriverProxies () {
  this.suspendChromedriverProxy(); // make sure we turn off the proxy flag
  for (let context of _.keys(this.sessionChromedrivers)) {
    let cd = this.sessionChromedrivers[context];
    log.debug(`Stopping chromedriver for context ${context}`);
    // stop listening for the stopped state event
    cd.removeAllListeners(Chromedriver.EVENT_CHANGED);
    try {
      await cd.stop();
    } catch (err) {
      log.warn(`Error stopping Chromedriver: ${err.message}`);
    }
    delete this.sessionChromedrivers[context];
  }
};

// For now the only known arg passed this way is androidDeviceSocket used
  // by Operadriver (deriving from Chromedriver) // We don't know how other
  // Chromium embedders will call this argument so for now it's name needs to
  // be configurable. When Google adds the androidDeviceSocket argument to
  // the original Chromedriver then we will be sure about its name for all
  // Chromium embedders (as their Webdrivers will derive from Chromedriver)
  if (this.args.specialChromedriverSessionArgs) {
    _.each(this.args.specialChromedriverSessionArgs, function (val, option) {
      logger.debug("This method is being deprecated. Apply chromeOptions " +
                   "normally to pass along options,see sites.google.com/a/" +
                   "chromium.org/chromedriver/capabilities for more info");
      caps.chromeOptions[option] = val;
    });
  }
  caps = this.decorateChromeOptions(caps);
  this.chromedriver.on(Chromedriver.EVENT_CHANGED, function (msg) {
    if (msg.state === Chromedriver.STATE_STOPPED) {
      // bind our stop/exit handler, passing in context so we know which
      // one stopped unexpectedly
      this.onChromedriverStop(context);
    }
  }.bind(this));
  this.chromedriver.start(caps).nodeify(function (err) {
    if (err) return cb(err);
    // save the chromedriver object under the context
    this.sessionChromedrivers[context] = this.chromedriver;
    cb();
  }.bind(this));
};

it('should handle chromedriver event with STATE_STOPPED state', async function () {
      await driver.startChromedriverProxy('WEBVIEW_1');
      await driver.chromedriver.emit(Chromedriver.EVENT_CHANGED,
        {state: Chromedriver.STATE_STOPPED});
      driver.onChromedriverStop.calledWithExactly('WEBVIEW_1').should.be.true;
    });
    it('should ignore events if status is not STATE_STOPPED', async function () {

it('should ignore events if status is not STATE_STOPPED', async function () {
      await driver.startChromedriverProxy('WEBVIEW_1');
      await driver.chromedriver.emit(Chromedriver.EVENT_CHANGED,
        {state: 'unhandled_state'});
      driver.onChromedriverStop.notCalled.should.be.true;
    });
    it('should reconnect if session already exists', async function () {

}
  };
  if (this.args.enablePerformanceLogging) {
    caps.loggingPrefs = {performance: 'ALL'};
  }

  var knownPackages = ["org.chromium.chrome.shell",
                       "com.android.chrome",
                       "com.chrome.beta"];

  if (!_.contains(knownPackages, this.args.appPackage)) {
    caps.chromeOptions.androidActivity = this.args.appActivity;
  }

  caps = this.decorateChromeOptions(caps);
  this.chromedriver.on(Chromedriver.EVENT_CHANGED, function (msg) {
    if (msg.state === Chromedriver.STATE_STOPPED) {
      logger.info("Chromedriver stopped unexpectedly on us, shutting down " +
                  "then calling back up with the on-die callback");
      this.onChromedriverStop(this.onDieCb);
    }
  }.bind(this));
  this.chromedriver.start(caps).nodeify(function (err) {
    if (err) return cb(err);
    cb(null, this.chromedriver.sessionId());
  }.bind(this));
};