RailsAbTest

Perform A/B Testing in your Rails app with ease.

The idea is a combination of

• minimal Code to support A/B Test versioning, is provided by this gem.
• A simple Pattern to organize the code in views into separated versions for each A/B Test version.

Add this line to your application's Gemfile:

gem 'rails_ab_test'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails_ab_test

Let's start with the simplest usage case:

Configure your controllers by including the module, normally ApplicationController is a good candidate for this:

include RailsAbTest::Controller

Then for the action (index in the example) that will be A/B Tested set a before_filter:

# a controller
before_filter :choose_ab_test, only: :index

The method choose_ab_test will randomly (with 50% probability) choose A or B as the A/B Test version. From here the version chosen will be accessible in your views and helpers in the variable @ab_test.

Then inside the action you need to replace render with render_ab

# a controller
def index
  render_ab
end

render_ab will infer the template to render from the action name, and prepend it with @ab_test to fully determine the template name. i.e. if the A/B Version is A it will render the template index_A.

Now you need to make 2 copies of your index view template, and name it index_A for the A/B Test version A, and index_B for B.

Make sure you set up different tracking for each version and you are good to go. Your controller's index action is ready to be A/B Tested.

For testing and QA purposes the A/B Test version can be selected by appending ?ab_test=A to the url of the page, that will make sure the version A is selected.

Then instead of a before_filter you can call the method choose_ab_test directly:

# a controller
def show
  choose_ab_test ['A', 'B', 'C'] # this action calls the method directly instead
  render_ab
end

Again the 3 versions will have the same probability of being chosen.

NOTE: in the current version the gem only supports versions with equal probabilities each.

Imagine that the actions index and archive are both A/B versioned and they share the same template. The action index will not change, but archive needs to explicitly render the index template like this:

# a controller
before_filter :choose_ab_test, only: :index, :archive

def archive
  render_ab template: 'index'
end

If instead of a full page template only a partial is going to be A/B Tested, you can achieve like this:

# index.haml.html template
= render_ab partial: 'menu', variable_for_the_partial: @variable

The pattern again here is to make 2 copies of the _menu partial and name them, i.e. _menu_A and _menu_B.

Based on the variable @ab_test you can also make conditions in views and helpers:

# index.haml.html template
- if @ab_test == 'A'
  version A is rendered
- else
  hello B

# a view helper
def helper_method_AB_versioned
  if @ab_test == 'A'
    'version A is rendered'
  else
    'Hello B'
  end
end

Now imagine that the index actions of 2 controllers (e.g. posts and authors) are A/B versioned, and that you want that when an user sees version A of posts#index she should also see version A of authors#index.

This can be achieved by overriding the method choose_ab_test in both controllers, and using a cookie:

# posts controller
before_filter :choose_ab_test, only: :index

...

def choose_ab_test
  @ab_test = cookies['shared-version-posts-authors'] || super
  cookies['shared-version-posts-authors'] = @ab_test
end

# authors controller should have the same code as above

Of course you can extract the common code to a central place. Also name the cookie with a name that makes sense for you, and expire it, sign it or encrypt it as needed.

If an user should always see the same A/B version of a page, the same method above and a cookie work perfectly:

# a controller
before_filter :choose_ab_test, only: :index

...

def choose_ab_test
  @ab_test = cookies['shared-version-posts-authors'] || super
  cookies['shared-version-posts-authors'] = @ab_test
end

Bug reports and pull requests are welcome on GitHub at https://github.com/joahking/rails_ab_test.

• write tests

The gem is available as open source under the terms of the MIT License.