factory_girl

Written by Joe Ferris.

Thanks to Tammer Saleh, Dan Croak, and Jon Yurek of thoughtbot, inc.

Copyright 2008 Joe Ferris and thoughtbot, inc.

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Gem:

gem install thoughtbot-factory_girl --source http://gems.github.com

Note: if you install factory_girl using the gem from Github, you’ll need this in your environment.rb if you want to use Rails 2.1’s dependency manager:

config.gem “thoughtbot-factory_girl”, :lib => “factory_girl”, :source => “http://gems.github.com”

Defining factories

# This will guess the User class
Factory.define :user do |u|
  u.first_name 'John'
  u.last_name  'Doe'
  u.admin false
end

# This will use the User class (Admin would have been guessed)
Factory.define :admin, :class => User do |u|
  u.first_name 'Admin'
  u.last_name  'User'
  u.admin true
end

It is recommended that you create a test/factories.rb file and define your factories there. This file can be included from test_helper or directly from your test files. Don’t forget:

require 'factory_girl'

Lazy Attributes

Most attributes can be added using static values that are evaluated when the factory is defined, but some attributes (such as associations and other attributes that must be dynamically generated) will need values assigned each time an instance is generated. These “lazy” attributes can be added by passing a block instead of a parameter:

Factory.define :user do |u|
  # ...
  u.activation_code { User.generate_activation_code }
end

Dependent Attributes

Some attributes may need to be generated based on the values of other attributes. This can be done by calling the attribute name on Factory::AttributeProxy, which is yielded to lazy attribute blocks:

Factory.define :user do |u|
  u.first_name 'Joe'
  u.last_name  'Blow'
  u.email {|a| "#{a.first_name}.#{a.last_name}@example.com".downcase }
end

Factory(:user, :last_name => 'Doe').email
# => "joe.doe@example.com"

Associations

Associated instances can be generated by using the association method when defining a lazy attribute:

Factory.define :post do |p|
  # ...
  p.author {|author| author.association(:user, :last_name => 'Writely') }
end

When using the association method, the same build strategy (build, create, or attributes_for) will be used for all generated instances:

# Builds and saves a User and a Post
post = Factory(:post)
post.new_record?       # => false
post.author.new_record # => false

# Builds but does not save a User and a Post
Factory.build(:post)
post.new_record?       # => true
post.author.new_record # => true

Because this pattern is so common, a prettier syntax is available for defining associations:

# The following definitions are equivilent:
Factory.define :post do |p|
  p.author {|a| a.association(:user) }
end

Factory.define :post do |p|
  p.association :author, :factory => :user
end

If the factory name is the same as the association name, the factory name can be left out.

Sequences

Unique values in a specific format (for example, e-mail addresses) can be generated using sequences. Sequences are defined by calling Factory.sequence, and values in a sequence are generated by calling Factory.next:

# Defines a new sequence
Factory.sequence :email do |n|
  "person#{n}@example.com" 
end

Factory.next :email
# => "person1@example.com" 

Factory.next :email
# => "person2@example.com"

Using factories

# Build and save a User instance
Factory(:user)

# Build a User instance and override the first_name property
Factory.build(:user, :first_name => 'Joe')

# Return an attributes Hash that can be used to build a User instance
attrs = Factory.attributes_for(:user)

More Information

Our blog

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