factory_bot.md

FactoryBot

Defining factories

FactoryBot.define do

  # Default 
  # It will use the User class
  factory :user do
    first_name { "John" }
    last_name { "Doe" }
    admin { false }
  end

  # Specifying the class 
  # It will use the User class, instead of Admin class
  factory :admin, class: User do
    first_name { "Admin" }
    last_name { "User" }
    admin { true }
  end

end

Building factories

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

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

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

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

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

# Overriding attributes of a factory
user = FactoryBot.build(:user, first_name: "Joe")
user.first_name
# => "Joe"

# No matter which build strategy is used to override attributes
user = FactoryBot.create(:user, first_name: "Joe")
user.first_name
# => "Joe"

Dependent attributes

Attributes can be based on the values of other attributes.

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

Associations

# If the factory name is the same as the association name, it's simple
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

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

Aliases

Aliases allow 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
  # instead of association :author, factory: :user
  author
  title { "How to read a book effectively" }
  body { "There are five steps involved." }
end

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

Trait

Trait helps you to remove duplication

FactoryBot.define do
  factory :post do
    title { 'An awesome post' }
    body { 'Lorem Ipsum...' }

    trait :published do
      status { :published }
    end

    trait :unpublished do
      status { :draft }
    end
    
    trait :with_comments do
      after(:create) do |post|
        create_list :comment, 2, todo_item: post
      end
    end
  end
end

# then in your test

let(:post) { create(:post, :published) }

# or even with

let(:post) { create(:post, :published, :with_comments) }