[Rails] Factory bot cheat sheet

factory-bot-cheat-sheet.rb

# spec/fixtures/usernames.rb
USERNAMES = ['hermione.granger',
             'ron.weasley',
             'harry.potter',
             'fred.weasley',
             'georges.weasley',
             'luna.lovegood',
             'ginny.weasley',
             'draco.malfoy',
             'albus.dumbledore',
             'hannah.abbott',
             'godric.gryffindor',
             'helga.hufflepuff',
             'neville.longbottom',
             'remus.lupin']

# spec/factory/user.rb
require 'fixtures/usernames'

FactoryBot.define do
  # sequence
  sequence :email do |n|
    username = USERNAMES[n] || "wizard_#{n}"

    "#{username}@hogwarts.wiz"
  end

  # aliases
  factory :user, aliases: [:owner] do
    email
  end
  
  # trait
  trait :with_books do
    items { create_list :book, 3 }
  end
  
  # many-to-many relationship: create without existing resources
  trait :with_bedrooms do
    after :create do |user|
      user.bedrooms = create_list :bedroom, 3
    end
  end
  
  # many-to-many relationhsip: create with existing resources
  transient do
    taught_by nil
  end
  
  after(:create) do |user, factory|
    if taught_by
      create(:mentorship, user: user, professor: factory.taught_by)
    end
  end
  
  # by-passing validations
  factory :user do
    …
    
    to_create { |instance| instance.save(validate: false) }
  end
  
  # custom factory name
  factory :bare_user, class: User do
    …
  end
  
  # using Active Storage
  factory :user do
    …
    
    after :build do |user|
      user.image.attach(
        io: File.open('spec', 'fixtures', 'files', 'YOUR_FILE.jpg'),
        filename: 'YOUR_FILE.jpg',
        content_type: 'image/jpeg',
       )
    end
  end
end