Experimental Build Status Code Climate

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


rails g experimental


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
  # ...


Create an experiment

In config/experimental.yml, add the name, num_buckets, and notes of the experiment under 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.not_in_experiment?(:my_experiment) # inverse

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


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.

  name: :price_experiment

Then run rake experimental:sync


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).


require 'experimental/test/unit'

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

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


require 'experimental/test/rspec'

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


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.


When you deploy, simply invoke the experimental:sync Rake task to update the experiments in your database from the configuration file:

after 'deploy:updated', 'experimental:sync' do
  on primary :worker do
    within release_path do
      rake experimental:sync

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.