Factory Bot (Rails Testing)

Factory Bot, originally known as Factory Girl, is a software library for the Ruby programming language that provides factory methods to create test fixtures for automated software testing. The fixture objects can be created on the fly; they may be plain Ruby objects with a predefined state, ORM objects with existing database records or mock objects.

Factory Bot is often used in testing Ruby on Rails applications; where it replaces Rails' built-in fixture mechanism. Rails' default setup uses a pre-populated database as test fixtures, which are global for the complete test suite. Factory Bot, on the other hand, allows developers to define a different setup for each test and thus helps to avoid dependencies within the test suite.

Factories

Defining Factories

A factory is defined by a name and its set of attributes. The class of the test object can is either determined through the name of the factory or set explicitly.

 FactoryBot.define do
   # Determine class automatically
   factory :user do
     name = "Captain Minion"
     superhero false
   end
   
   # Specific class explicitly
   factory :superhero, class: User do
     name = "[[Tony Stark]]"
     superhero true
   end
 end

Features

Traits

Traits allow grouping of attributes which can be applied to any factory.

 '''factory''' :status '''do''' 
   title "Seeking for Full Time jobs"
 
   '''trait''' :international '''do'''
 	international true
   '''end'''
 
   '''trait''' :resident '''do'''
 	international false
   '''end'''
 
   '''trait''' :comp_sci '''do'''
 	comp_sci true
   '''end'''
 
   '''trait''' :electrical '''do'''
 	comp_sci false
   '''end'''
 	
   '''factory''' :comp_sci_international_student,  traits: [:international, :comp_sci]
   '''factory''' :electrical_resident_student,  traits: [:resident, :electrical]
 '''end'''

Alias

Factory Bot allows creating aliases for existing factories so that the factories can be reused.

factory :user, aliases: [:student, :teacher] do
 first_name    "John"
end

factory :notice do
 teacher
 # Alias used teacher for user
 title "Office Hours"
end

factory :notification do
 student
 #Alias used student for user 
 title "Lecture timings"
end

Sequences

Factory Bot allows creating unique values for a test attribute in a given format.

 FactoryBot.define do
   factory :title do
     sequence(:name) {|n| "Title #{n}" }
     # Title 1, Title 2 and so on...
   end
 end

Inheritance

Factories can be inherited while creating a factory for a class. This allows the user to reuse common attributes from parent factories and avoid writing duplicate code for duplicate attributes. Factories can be written in a nested fashion to leverage inheritance.

factory :user do
   name "Micheal"

   factory :admin do
       admin_rights true
   end
end

admin_user = create(:admin)
admin_user.name   # Micheal
admin_user.admin_rights   # true

Parent factories can also be specified explicitly.

factory :user do
  name "Micheal"
end

factory :admin, parent: :user do
  admin_user true
end

Callback

Factory Bot allows custom code to be injected at four different stages:

after(:build)

Code can be injected after the factory is built

before(:create)

Code can be injected before the factory is saved

after(:create)

Code can be injected after the factory is saved

after(:stub)

Code can be injected before the factory is stubbed

See also

Other Test libraries for Ruby

• NullDB: a way to speed up testing by avoiding database use.
• Fixture Builder: a tool that compiles Ruby factories into fixtures before a test run.
• Shoulda: an extension to test/unit with additional helpers, macros, and assertions.
• Rspec: a behavior-driven development framework
• Capybara: Acceptance test framework for web applications.