thoughtbot--factory_bot/GETTING_STARTED.md

Getting Started

Update Your Gemfile

If you're using Rails, you'll need to change the required version of factory_girl_rails:

gem "factory_girl_rails", "~> 1.2"

If you're not using Rails, you'll just have to change the required version of factory_girl:

gem "factory_girl", "~> 2.1.0"

Once your Gemfile is updated, you'll want to update your bundle.

Defining factories

Each factory has a name and a set of attributes. The name is used to guess the class of the object by default, but it's possible to explicitly specify it:

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

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

  # The same, but using a string instead of class constant
  factory :admin, :class => 'user' do
    first_name 'Admin'
    last_name  'User'
    admin true
  end
end

It is highly recommended that you have one factory for each class that provides the simplest set of attributes necessary to create an instance of that class. If you're creating ActiveRecord objects, that means that you should only provide attributes that are required through validations and that do not have defaults. Other factories can be created through inheritance to cover common scenarios for each class.

Attempting to define multiple factories with the same name will raise an error.

Factories can be defined anywhere, but will be automatically loaded if they are defined in files at the following locations:

test/factories.rb
spec/factories.rb
test/factories/*.rb
spec/factories/*.rb

Using factories

factory_girl supports several different build strategies: build, create, attributes_for and stub:

# Returns a User instance that's not saved
user = FactoryGirl.build(:user)

# Returns a saved User instance
user = FactoryGirl.create(:user)

# Returns a hash of attributes that can be used to build a User instance
attrs = FactoryGirl.attributes_for(:user)

# Returns an object with all defined attributes stubbed out
stub = FactoryGirl.build_stubbed(:user

# Passing a block to any of the methods above will yield the return object
FactoryGirl.create(:user) do |user|
  user.posts.create(attributes_for(:post))
end

No matter which strategy is used, it's possible to override the defined attributes by passing a hash:

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

If repeating "FactoryGirl" is too verbose for you, you can mix the syntax methods in:

# rspec
RSpec.configure do |config|
  config.include Factory::Syntax::Methods
end

# Test::Unit
class Test::Unit::TestCase
  include Factory::Syntax::Methods
end

This would allow you to write:

describe User, "#full_name" do
  subject { create(:user, :first_name => "John", :last_name => "Doe") }

  its(:full_name) { should == "John Doe" }
end

Lazy Attributes

Most factory 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 :user do
  # ...
  activation_code { User.generate_activation_code }
  date_of_birth   { 21.years.ago }
end

Aliases

Aliases allow you to use named associations more easily.

factory :user, :aliases => [:author, :commenter] do
  first_name    "John"
  last_name     "Doe"
  date_of_birth { 18.years.ago }
end

factory :post do
  author
  # instead of
  # association :author, :factory => :user
  title "How to read a book effectively"
  body  "There are five steps involved."
end

factory :comment do
  commenter
  # instead of
  # association :commenter, :factory => :user
  body "Great article!"
end

Dependent Attributes

Attributes can be based on the values of other attributes using the proxy that is yielded to lazy attribute blocks:

factory :user do
  first_name 'Joe'
  last_name  'Blow'
  email { "#{first_name}.#{last_name}@example.com".downcase }
end

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

Transient Attributes

There may be times where your code can be DRYed up by passing in transient attributes to factories.

factory :user do
  ignore do
    rockstar true
    upcased { false }
  end

  name  { "John Doe#{" - Rockstar" if rockstar}" }
  email { "#{name.downcase}@example.com" }

  after_create do |user, proxy|
    user.name.upcase! if proxy.upcased
  end
end

FactoryGirl.create(:user, :upcased => true).name
#=> "JOHN DOE - ROCKSTAR"

Static and dynamic attributes can be ignored. Ignored attributes will be ignored within attributes_for and won't be set on the model, even if the attribute exists or you attempt to override it.

Within Factory Girl's dynamic attributes, you can access ignored attributes as you would expect. If you need to access the proxy in a Factory Girl callback, you'll need to declare a second block argument (for the proxy) and access ignored attributes from there.

Associations

It's possible to set up associations within factories. If the factory name is the same as the association name, the factory name can be left out.

factory :post do
  # ...
  author
end

You can also specify a different factory or override attributes:

factory :post do
  # ...
  association :author, :factory => :user, :last_name => 'Writely'
end

The behavior of the association method varies depending on the build strategy used for the parent object.

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

# Builds and saves a User, and then builds but does not save a Post
post = FactoryGirl.build(:post)
post.new_record?        # => true
post.author.new_record? # => false

To not save the associated object, specify :method => :build in the factory:

factory :post do
  # ...
  association :author, :factory => :user, :method => :build
end

# Builds a User, and then builds a Post, but does not save either
post = FactoryGirl.build(:post)
post.new_record?        # => true
post.author.new_record? # => true

Inheritance

You can easily create multiple factories for the same class without repeating common attributes by nesting factories:

factory :post do
  title 'A title'

  factory :approved_post do
    approved true
  end
end

approved_post = FactoryGirl.create(:approved_post)
approved_post.title # => 'A title'
approved_post.approved # => true

You can also assign the parent explicitly:

factory :post do
  title 'A title'
end

factory :approved_post, :parent => :post do
  approved true
end

As mentioned above, it's good practice to define a basic factory for each class with only the attributes required to create it. Then, create more specific factories that inherit from this basic parent. Factory definitions are still code, so keep them DRY.

Sequences

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

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

FactoryGirl.generate :email
# => "person1@example.com"

FactoryGirl.generate :email
# => "person2@example.com"

Sequences can be used as attributes:

factory :user do
  email
end

Or in lazy attributes:

factory :invite do
  invitee { FactoryGirl.generate(:email) }
end

And it's also possible to define an in-line sequence that is only used in a particular factory:

factory :user do
  sequence(:email) {|n| "person#{n}@example.com" }
end

You can also override the initial value:

factory :user do
  sequence(:email, 1000) {|n| "person#{n}@example.com" }
end

Without a block, the value will increment itself, starting at its initial value:

factory :post do
  sequence(:position)
end

Traits

Traits allow you to group attributes together and then apply them to any factory.

factory :user, :aliases => [:author]

factory :story do
  title "My awesome story"
  author

  trait :published do
    published true
  end

  trait :unpublished do
    published false
  end

  trait :week_long_publishing do
    start_at { 1.week.ago }
    end_at   { Time.now }
  end

  trait :month_long_publishing do
    start_at { 1.month.ago }
    end_at   { Time.now }
  end

  factory :week_long_published_story,    :traits => [:published, :week_long_publishing]
  factory :month_long_published_story,   :traits => [:published, :month_long_publishing]
  factory :week_long_unpublished_story,  :traits => [:unpublished, :week_long_publishing]
  factory :month_long_unpublished_story, :traits => [:unpublished, :month_long_publishing]
end

Traits can be used as attributes:

factory :week_long_published_story_with_title, :parent => :story do
  published
  week_long_publishing
  title { "Publishing that was started at {start_at}" }
end

Traits that define the same attributes won't raise AttributeDefinitionErrors; the trait that defines the attribute latest gets precedence.

factory :user do
  name "Friendly User"
  login { name }

  trait :male do
    name   "John Doe"
    gender "Male"
    login { "#{name} (M)" }
  end

  trait :female do
    name   "Jane Doe"
    gender "Female"
    login { "#{name} (F)" }
  end

  trait :admin do
    admin true
    login { "admin-#{name}" }
  end

  factory :male_admin,   :traits => [:male, :admin]   # login will be "admin-John Doe"
  factory :female_admin, :traits => [:admin, :female] # login will be "Jane Doe (F)"
end

You can also override individual attributes granted by a trait in subclasses.

factory :user do
  name "Friendly User"
  login { name }

  trait :male do
    name   "John Doe"
    gender "Male"
    login { "#{name} (M)" }
  end

  factory :brandon do
    male
    name "Brandon"
  end
end

Callbacks

factory_girl makes available three callbacks for injecting some code:

• after_build - called after a factory is built (via FactoryGirl.build)
• after_create - called after a factory is saved (via FactoryGirl.create)
• after_stub - called after a factory is stubbed (via FactoryGirl.stub)

Examples:

# Define a factory that calls the generate_hashed_password method after it is built
factory :user do
  after_build { |user| generate_hashed_password(user) }
end

Note that you'll have an instance of the user in the block. This can be useful.

You can also define multiple types of callbacks on the same factory:

factory :user do
  after_build  { |user| do_something_to(user) }
  after_create { |user| do_something_else_to(user) }
end

Factories can also define any number of the same kind of callback. These callbacks will be executed in the order they are specified:

factory :user do
  after_create { this_runs_first }
  after_create { then_this }
end

Calling FactoryGirl.create will invoke both after_build and after_create callbacks.

Also, like standard attributes, child factories will inherit (and can also define) callbacks from their parent factory.

Modifying factories

If you're given a set of factories (say, from a gem developer) but want to change them to fit into your application better, you can modify that factory instead of creating a child factory and adding attributes there.

If a gem were to give you a User factory:

FactoryGirl.define do
  factory :user do
    full_name "John Doe"
    sequence(:username) {|n| "user#{n}" }
    password "password"
  end
end

Instead of creating a child factory that added additional attributes:

FactoryGirl.define do
  factory :application_user, :parent => :user do
    full_name     { Faker::Name.name }
    date_of_birth { 21.years.ago }
    gender        "Female"
    health        90
  end
end

You could modify that factory instead.

FactoryGirl.modify do
  factory :user do
    full_name     { Faker::Name.name }
    date_of_birth { 21.years.ago }
    gender        "Female"
    health        90
  end
end

When modifying a factory, you can change any of the attributes you want (aside from callbacks).

FactoryGirl.modify must be called outside of a FactoryGirl.define block as it operates on factories differently.

A caveat: you can only modify factories (not sequences or traits) and callbacks still compound as they normally would. So, if the factory you're modifying defines an after_create callback, you defining an after_create won't override it, it'll just get run after the first callback.

Building or Creating Multiple Records

Sometimes, you'll want to create or build multiple instances of a factory at once.

built_users   = FactoryGirl.build_list(:user, 25)
created_users = FactoryGirl.create_list(:user, 25)

These methods will build or create a specific amount of factories and return them as an array. To set the attributes for each of the factories, you can pass in a hash as you normally would.

twenty_year_olds = FactoryGirl.build_list(:user, 25, :date_of_birth => 20.years.ago)

Cucumber Integration

factory_girl ships with step definitions that make calling factories from Cucumber easier. To use them, add the following to features/support/env.rb:

require 'factory_girl/step_definitions'

Alternate Syntaxes

Users' tastes for syntax vary dramatically, but most users are looking for a common feature set. Because of this factory_girl supports "syntax layers" which provide alternate interfaces. See Factory::Syntax for information about the various layers available. For example, the Machinist-style syntax is popular:

require 'factory_girl/syntax/blueprint'
require 'factory_girl/syntax/make'
require 'factory_girl/syntax/sham'

Sham.email {|n| "#{n}@example.com" }

User.blueprint do
  name  { 'Billy Bob' }
  email { Sham.email  }
end

User.make(:name => 'Johnny')