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Poltergeist with Rails and Angular

23 Feb 2015

This past week I worked on converting a Rails and Angular application that was using Selenium as the driver for Spinach/Capybara tests over to using Poltergeist.

The change was motivated by the fact that our Spinach tests using Selenium where taking an average of 4 minutes to run. That's not terrible, but could definitely be improved. Also, I wanted to look into running tests in parallel which would be easier with a headless driver.

Spoiler alert: 2x speed improvement ahead.

Getting PhantomJS Running

When I first switched our tests over to using Poltergeist I noticed that even though links where being clicked ui-router was not transitioning to the new state.

After some digging I realized the issue was that PhantomJS does not support Function.prototype.bind in 1.9.x versions and our app had code in the resolve section of our states was using bind. When calling bind failed the state transition would be halted.

The solution is to add a polyfill such as this bower package which can be installed using Rails Assets.

# Gemfile
source 'https://rails-assets.org'
gem 'rails-assets-bind-polyfill'

# application.js
//= require bind-polyfill

Throwing Errors

By default Poltergeist does not re-raise errors, however, having this turned on is usually helpful in finding errors. Angular makes this a challenge though: instead of throwing errors it catches them using the $exceptionHandler service and logs them. If we want to be able to re-raise errors we will need to load an extension for Poltergeist.

# features/support/env.rb
Capybara.register_driver :poltergeist do |app|
    extensions: [ 'features/support/angular_errors.js' ],
    js_errors:   true

In our extension we can redefine the error function on the $log service to instead throw an exception. Original script taken from the Localytics blog.

I also added void implementations for $log.info and $log.debug to clean up test output as our app logs every state transition with debugging information.

// features/support/angular_errors.js
window.onload = function() {
  var $injector = angular.element(document).injector();
  var $log = $injector.get('$log');

  // Raise Angular errors
  $log.error = function(error) { throw(error); };

  // Suppress Angular Logging
  $log.info = function () {};
  $log.debug = function () {};


One thing that's always hard with a headless browser is to see what's going on when the test is interacting with the page. For basic debugging, I've found that taking a screenshot using the save_screenshot method while in a Pry session of stepping through your tests works well.

save_screenshot('/Users/caleb/Desktop/debug.png', full: true)

For debugging tests that don't have driver specific issues I still like to use Selenium so that you can click around the page. So I created a hook to switch the driver any time the @selenium tag is added to a scenario.

Spinach.hooks.on_tag('selenium') do
  Capybara.current_driver = :selenium

2x Speed Improvement

After fixing a couple of tests that used features of Capybara specific to Selenium and some issues with mouse events, I was able to run the entire test suite with Poltergeist.

With these changes in place running Spinach tests, which took 4 minutes using Selenium, now took just 2 minutes. Well worth the effort.

Edit 2015-02-24: Today after upgrading PhantomJS to version 2.0.0 I'm seeing even more remarkable speed improvements. The same Spinach tests now run in about 75 seconds. Overall a 3.2x improvement from using Selenium.