Everyday Rails

Switching from Selenium to Poltergeist in RSpec feature specs

By Aaron Sumner, January 27, 2015. File under: , .

I was recently asked about how I test JavaScript-dependent features in RSpec. In Everyday Rails Testing with RSpec, I demonstrate using Selenium for this type of test. As I note there, though, and as you’ve no doubt found for yourself, spawning a browser window each time is slow. It’s also not compatible with continuous integration services like Jenkins or Travis CI. That’s where headless drivers like Poltergeist and capybara-webkit come into play. They’re capable of running JavaScript, like Selenium, but don’t require an external browser.

In my own work, I use Poltergeist for these tests. Poltergeist is a Ruby wrapper for the PhantomJS headless browser, so you’ll have to install PhantomJS first. I recommend using your operating system’s built-in package manager to do this, when possible. On my Mac, I use Homebrew (brew install phantomjs). If you’re on Windows, or just not sure, download and run the installer.

With installation out of the way, you can now install Poltergeist and configure it to be your test suite’s driver for JavaScript-dependent tests. First, add it to your Gemfile:

group :test do
  # Other testing gems ...
  gem 'poltergeist'
  # Go ahead and remove selenium-webdriver, if needed

Run bundle install to install the gem.

Next, configure RSpec to use it. Add the following to your spec/rails_helper.rb file. (If you’re still using RSpec 2.x, you’ll add this to spec/spec_helper.rb):

require 'capybara/poltergeist'
Capybara.javascript_driver = :poltergeist

Now, run your test suite–or at least run your feature specs, or your feature specs that require JavaScript. If everything is set up correctly, you should see them run in your terminal, but not in a Firefox window.

In addition to speeding up your test runs, Poltergeist provides some advanced features. I don’t use these often, but they are handy from time to time, particularly for debugging tests. I encourage you to refer to Poltergeist’s README to learn more.

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