« 25 Days of Ruby Gems - Ruby Advent Calendar 2020, December 1st - December 25th

Day 5 - factory_bot Gem - “Hey, Make Me a User with an Email and Password” - Setup Factories That Make You Fake Objects with Fake Data for Testing

Written by JasonSwett Jason Swett

Blogs about Ruby on Rails Testing, speaks at international conferences and hosts the Rails with Jason Podcast.

Creating test data without headaches

factory_bot is a fixtures replacement with a straightforward definition syntax, support for multiple build strategies (saved instances, unsaved instances, attribute hashes, and stubbed objects), and support for multiple factories for the same class (user, admin_user, and so on), including factory inheritance.

There are three steps I go through to set up Factory Bot in a Rails application.

  1. Install the factory_bot_rails gem
  2. Set up one or more factory definitions
  3. Add the Factory Bot syntax methods to my rails_helper.rb file

Install the factory_bot_rails gem

The first thing I do is to include the factory_bot_rails gem (not the factory_bot gem) in my Gemfile. I include it under the :development, :test group.

Here’s a sample Gemfile from a project with only the default gems plus a few that I added for testing.

Remember that after you add a gem to your Gemfile you’ll need to run bundle install in order to actually install the gem.

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.7.0'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 6.0.2', '>='
# Use postgresql as the database for Active Record
gem 'pg', '>= 0.18', '< 2.0'
# Use Puma as the app server
gem 'puma', '~> 4.1'
# Use SCSS for stylesheets
gem 'sass-rails', '>= 6'
# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
gem 'webpacker', '~> 4.0'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder

gem 'devise'

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.4.2', require: false

group :development, :test do
  gem 'pry'
  gem 'rspec-rails'
  gem 'capybara'
  gem 'webdrivers'
  gem 'factory_bot_rails'

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background...
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

Set up one or more factory definitions

Factory definitions are kind of the “templates” that are used for generating new objects.

For example, I have a user object that needs an email and a password, then I would create a factory definition saying “hey, make me a user with an email and password”. The actual code might look like this:

FactoryBot.define do
  factory :user do
    email { 'test@example.com' }
    password { 'password1' }

Factory Bot is smart enough to know that when I say factory :user do, I’m talking about an Active Record class called User.

There’s a problem with this way of defining my User factory though. If I have a unique constraint on the users.email column in the database (for example), then I won’t ever be able to generate more than one User object. The first user’s email address will be test@example.com (no problem so far) but then when I go to create a second user, its email address will also be test@example.com, and if I have a unique constraint on users.email, the creation of this second record will not be allowed.

We need a way of making it so the factories’ values can be unique. One way, which I’ve done before, is to append a random number to the end of the email address, e.g. "test#{SecureRandom.hex}@example.com". There’s a different way to do it, though, that I find nicer. That way is to use another gem called Faker.

Add the Factory Bot syntax methods to my rails_helper.rb file

The syntax for actually using a Factory Bot factory in a test is as follows:


There’s nothing wrong with this, but I find that these FactoryBot are so numerous in my test files that their presence feels a little noisy.

There’s a way to make it so that instead we can just write this:


The way to do that is to add a bit of code to spec/rails_helper.rb.

RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods

(You don’t actually add the RSpec.configure do |config| to the spec/rails_helper.rb file. It’s already there. I’m just including it here to show that that’s the block inside of which the config.include FactoryBot::Syntax::Methods line goes.)

Find Out More


Built with Ruby (running Jekyll) on 2021-07-25 15:15:02 +0000 in 0.371 seconds.
Hosted on GitHub Pages. </> Source on GitHub. (0) Dedicated to the public domain.