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", "~> 3.0"

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

gem "factory_girl", "~> 3.0"

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
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 FactoryGirl::Syntax::Methods
end

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

# Cucumber
World(FactoryGirl::Syntax::Methods)

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

In addition to running other methods dynamically, you can use FactoryGirl's syntax methods (like build, create, and generate) within dynamic attributes without having to prefix the call with FactoryGirl.. This allows you to do:

sequence(:random_string) {|n| LoremIpsum.generate }

factory :post do
  title { generate(:random_string) } # instead of FactoryGirl.generate(:random_string)
end

factory :comment do
  post
  body { generate(:random_string) }  # instead of FactoryGirl.generate(:random_string)
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 evaluator 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, evaluator|
    user.name.upcase! if evaluator.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 evaluator in a Factory Girl callback, you'll need to declare a second block argument (for the evaluator) 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 strategy: :build in the factory:

factory :post do
  # ...
  association :author, factory: :user, strategy: :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

Generating data for a has_many relationship is a bit more involved, depending on the amount of flexibility desired, but here's a surefire example of generating associated data.

FactoryGirl.define do

  # post factory with a `belongs_to` association for the user
  factory :post do
    title "Through the Looking Glass"
    user
  end

  # user factory without associated posts
  factory :user do
    name "John Doe"

    # user_with_posts will create post data after the user has been created
    factory :user_with_posts do
      # posts_count is declared as an ignored attribute and available in
      # attributes on the factory, as well as the callback via the evaluator
      ignore do
        posts_count 5
      end

      # the after_create yields two values; the user instance itself and the
      # evaluator, which stores all values from the factory, including ignored
      # attributes; `create_list`'s second argument is the number of records
      # to create and we make sure the user is associated properly to the post
      after_create do |user, evaluator|
        FactoryGirl.create_list(:post, evaluator.posts_count, user: user)
      end
    end
  end
end

This allows us to do:

FactoryGirl.create(:user).posts.length # 0
FactoryGirl.create(:user_with_posts).posts.length # 5
FactoryGirl.create(:user_with_posts, posts_count: 15).posts.length # 15

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 { 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

Sequences can also have aliases. The sequence aliases share the same counter:

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

# will increase value counter for :email which is shared by :sender and :receiver
FactoryGirl.next(:sender)

Define aliases and use default value (1) for the counter

factory :user do
  sequence(:email, aliases: [:sender, :receiver]) {|n| "person#{n}@example.com" }
end

Setting the value:

factory :user do
  sequence(:email, 'a', aliases: [:sender, :receiver]) {|n| "person#{n}@example.com" }
end

The value just needs to support the #next method. Here the next value will be 'a', then 'b', etc.

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

Traits can also be passed in as a list of symbols when you construct an instance from FactoryGirl.

factory :user do
  name "Friendly User"

  trait :male do
    name   "John Doe"
    gender "Male"
  end

  trait :admin do
    admin true
  end
end

# creates an admin user with gender "Male" and name "Jon Snow"
FactoryGirl.create(:user, :admin, :male, name: "Jon Snow")

This ability works with build, build_stubbed, attributes_for, and create.

create_list and build_list methods are supported as well. Just remember to pass the number of instances to create/build as second parameter, as documented in the "Building or Creating Multiple Records" section of this file.

factory :user do
  name "Friendly User"

  trait :admin do
    admin true
  end
end

# creates 3 admin users with gender "Male" and name "Jon Snow"
FactoryGirl.create_list(:user, 3, :admin, :male, name: "Jon Snow")

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.build_stubbed)

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)

Custom Construction

If you want to use factory_girl to construct an object where some attributes are passed to initialize or if you want to do something other than simply calling new on your build class, you can override the default behavior by defining initialize_with on your factory. Example:

# user.rb
class User
  attr_accessor :name, :email

  def initialize(name)
    @name = name
  end
end

# factories.rb
sequence(:name) {|n| "person#{n}@example.com" }

factory :user do
  ignore do
    name { Faker::Name.name }
  end

  email
  initialize_with { User.new(name) }
end

FactoryGirl.build(:user).name # Bob Hope

Notice that I ignored the name attribute. If you don't want attributes reassigned after your object has been instantiated, you'll want to ignore them.

Although factory_girl is written to work with ActiveRecord out of the box, it can also work with any Ruby class. For maximum compatibiltiy with ActiveRecord, the default initializer builds all instances by calling new on your build class without any arguments. It then calls attribute writer methods to assign all the attribute values. While that works fine for ActiveRecord, it actually doesn't work for almost any other Ruby class.

You can override the initializer in order to:

• Build non-ActiveRecord objects that require arguments to initialize
• Use a method other than new to instantiate the instance
• Do crazy things like decorate the instance after it's built

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")