Experimental

Experimental is an Split testing framework for Rails.
It was written with a few goals in mind:

• Split the users in a non-predictable pattern (i.e. half of the users won't always be in all experiments)
• Keep experiments and their start and end dates in the database
• Have a clear developer workflow, so that tests in the code are started in the database when the code goes out and tests that should be removed make the site explode
• Allow admins to end experiments and set a winner
• Cache the experiments

Installation

rails g experimental

Routes

resources :experiments, only: [:index, :new, :create] do
  collection do
    get :inactive
      post :set_winner
    end
  end

  namespace :singles_admin do
    resources :experiments, only: [:index, :new, :create] do
      collection do
        get :inactive
        post :set_winner
      end
    end
  end
end

Admin Frontend

Create your own admin controller:

class Admin::ExperimentsController < ApplicationController
  include Experimental::ControllerActions

  alias_method :index, :experiments_index
  alias_method :new, :experiments_new
  alias_method :set_winner, :experiments_set_winner

  def create
    if experiments_create
      redirect_to admin_experiments_path
    else
      render :new
    end
  end

  def base_resource_name
    "singles_admin_experiment"
  end
end

Using ActiveAdmin:

rails g active_admin:resource Experiment

require 'experimental/controller_actions'

ActiveAdmin.register Experimental::Experiment, as: "Experiment" do
  actions :index, :new, :create
  filter :name

  controller do
    class_eval do
      include Experimental::ControllerActions
    end

    def base_resource_name
      "admin_experiment"
    end

    def create
      if experiments_create
        redirect_to admin_experiments_path
      else
        render :new
      end
    end

    def new
      experiments_new
    end
  end

  # collection_actions force active_admin to create a route
  collection_action :set_winner, method: :post do
    experiments_set_winner
  end

  # can do this instead of the ended_or_removed scope below
  # you will need to add a link to inactive_admins_experiments_path
  #  in your view
  collection_action :inactive do
    experiments_inactive
    render template: 'admin/experiments/index'
  end

  scope :in_progress, :default => true do |experiments|
    experiments.in_progress
  end

  scope :ended_or_removed do |experiments|
    @include_inactive = true
    experiments.ended_or_removed
  end

  index do
    render template: 'admin/experiments/index'
  end

  form partial: 'new'
end

Views

create an index and new view in appropriate view folder, i.e.

app/views/admin/experiments/index.html.erb

<%= render partial: 'experimental/links' %>
<%= render partial: 'experimental/index' %>

app/views/admin/experiments/new.html.erb

<%= render partial: 'experimental/links' %>
<%= render partial: 'experimental/new' %>

Note: ActiveAdmin users will not need to include the links partials

Subject

For the class you'd like to be the subject of experiments, include the Experimental::Subject module in a model with an id and timestamps

class User < ActiveRecord::Base
  include Experimental::Subject
  # ...
end

Usage

Create an experiment

In config/experimental.yml, add the name, num_buckets, and notes of the experiment under in_code:

in_code:
-
  name: :price_experiment
  num_buckets: 2
  notes: |
    0: $22
    1: $19.99

Then run rake experimental:sync

Using the experiment

To see if a user is in the experiment population AND in a bucket:

# checks if the user is in the my_experiment population
# and if they are in bucket 0
user.in_bucket?(:my_experiment, 0)

To see if a user is in the experiment population ONLY

user.in_experiment?(:my_experiment)
user.not_in_experiment?(:my_experiment) # inverse

To see which bucket of an experiment a user is in:

user.experiment_bucket(:my_experiment)

Ending an experiment

You can end an experiment by setting the end_date. In the admin interface, there is a dropdown to set the end date. When ending an experiment you must set a winning bucket

Ending an experiment means that all users will be given the winning bucket

Removing an experiment

A removed experiment is an experiment that is not referenced anywhere in code. In fact, the framework will throw an exception if you reference an experiment that is not in code.

Removing an experiment from config/experimental.yml and running rake experimental:sync will remove the experiment and expire the cache.

removed:
-
  name: :price_experiment

Then run rake experimental:sync

Testing

In your test suite, you typically want to have an neutral starting state across all your tests. For experiments, this means all subjects are out of all experiments. You then opt a particular subject into a particular bucket for any experiment as your test requires.

Experimental ships with support to do this in a number of popular test frameworks. Setup instructions for each framework are in the following sections.

Once set up, you can then force a subject into a bucket for an experiment as follows:

set_experimental_bucket(subject, :my_experiment, 1)

If you set the bucket (1 in the above example) to nil, this means set the subject to be out of the experiment (the default state).

Minitest

require 'experimental/test/unit'

class MyTest < Test::Unit::TestCase
  include Experimental::Test::Unit
  ...
end

Note that if you define a setup method, then you must remember to call super (always good practice in general).

RSpec

require 'experimental/test/rspec'

RSpec.configure do |config|
  config.include Experimental::Test::RSpec
end

Cucumber

require 'experimental/test/cucumber'

Developer Workflow

Experiments can be defined in config/experimental.yml Running the rake task rake experimental:sync will load those experiments under 'in_code' into the database and set removed_at timestamp for those under 'removed'

You will likely want to automate the running of rake experimental:sync by adding to your deploy file.

Capistrano

In config/deploy.rb:

Create a namespace to run the task:

namespace :database do
  desc "Sync experiments"
  task :sync_from_app, roles: :db, only: { primary: true } do
    run "cd #{current_path} && RAILS_ENV=#{rails_env} bundle exec rake experimental:sync"
  end
end

Include that in the deploy:default task:

namespace :deploy do
  #...
  task :default do
    begin
      update_code
      migrate
      database.sync_from_app
      restart
    #...
    end
  end
end

Admin created experiments

The purpose of Admin created experiments are for experiments that will flow through to another system, such as an email provider. They likely start with a known string and are dynamically sent in code. Otherwise, Admin created experiments will do nothing as there is no code attached to them.