Chapter IV - Factory Bot and Faker

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Creating test data is a common need in testing. Instead of manually creating Ebook, User, and Purchase objects in every test, Factory Bot provides a flexible way to build test objects. Combined with Faker, you can generate realistic random data that makes your tests more robust.

In this chapter, you will learn how to set up and use Factory Bot with Faker to create test data for your ebook application.

Setup

Steps to implement:

Add factory_bot_rails gem to your Gemfile (:development, :test group)
Add faker gem to your Gemfile
Run bundle install

Configure Factory Bot in spec/rails_helper.rb:

RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods
end

Create spec/factories/ directory for your factory files

Reference: Factory Bot Rails

Basic Factories

Create factories for your ebook application models.

Steps to implement:

Create the User factory:

# spec/factories/users.rb
FactoryBot.define do
  factory :user do
    name { "John Doe" }
    email { "john@example.com" }
    password { "password123" }
    status { :enabled }
  end
end

Create the Ebook factory:

# spec/factories/ebooks.rb
FactoryBot.define do
  factory :ebook do
    title { "Ruby Programming Guide" }
    price { 19.99 }
    status { :draft }
    association :seller, factory: :user
  end
end

Use factories in tests:
build(:user) - creates an instance without saving
create(:user) - creates and saves to database
build_stubbed(:ebook) - creates a stub (faster, no DB)
attributes_for(:ebook) - returns a hash of attributes

Using Faker

Faker generates realistic random data. This prevents test failures due to uniqueness constraints.

Steps to implement:

Update User factory with Faker:

factory :user do
  name { Faker::Name.name }
  email { Faker::Internet.unique.email }
  password { Faker::Internet.password(min_length: 8) }
  status { :enabled }
end

Update Ebook factory with Faker:

factory :ebook do
  title { Faker::Book.title }
  description { Faker::Lorem.paragraph(sentence_count: 3) }
  price { Faker::Commerce.price(range: 9.99..99.99) }
  status { :draft }
  association :seller, factory: :user
end

Explore useful Faker generators for your ebook app:
Faker::Book.title - realistic book titles
Faker::Book.author - author names
Faker::Commerce.price - prices in range
Faker::Internet.email - email addresses
Faker::Lorem.paragraph - descriptions
Faker::Date.backward(days: 30) - past dates for purchases

Reference: Faker Ruby

Sequences

Use sequences to generate unique values when Faker isn't enough.

Steps to implement:

Create a sequence for unique emails:

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

Create a sequence for ebook titles:

factory :ebook do
  sequence(:title) { |n| "Ebook Volume #{n}" }
end

Associations

Factory Bot handles the relationships in your ebook application elegantly.

Steps to implement:

Define Ebook factory with seller association:

factory :ebook do
  title { Faker::Book.title }
  price { Faker::Commerce.price(range: 9.99..49.99) }
  association :seller, factory: :user
end

Define Purchase factory with all associations:

factory :purchase do
  association :buyer, factory: :user
  association :ebook
  purchased_at { Time.current }
  amount { ebook.price }
end

Override associations when creating:

seller = create(:user, name: "Seller Joe")
buyer = create(:user, name: "Buyer Jane")
ebook = create(:ebook, seller: seller, price: 29.99)
purchase = create(:purchase, buyer: buyer, ebook: ebook)

Traits

Traits allow you to define variations of your factories—perfect for ebook statuses and user roles.

Steps to implement:

Define traits for Ebook statuses:

factory :ebook do
  title { Faker::Book.title }
  price { Faker::Commerce.price(range: 9.99..49.99) }
  status { :draft }
  association :seller, factory: :user

  trait :draft do
    status { :draft }
  end

  trait :pending do
    status { :pending }
  end

  trait :published do
    status { :live }
  end

  trait :expensive do
    price { Faker::Commerce.price(range: 79.99..199.99) }
  end
end

Define traits for User roles:

factory :user do
  name { Faker::Name.name }
  email { Faker::Internet.unique.email }

  trait :seller do
    # Add seller-specific attributes if any
  end

  trait :buyer do
    # Add buyer-specific attributes if any
  end

  trait :disabled do
    status { :disabled }
  end
end

Use traits when building:

create(:ebook, :published)
create(:ebook, :published, :expensive)
create(:user, :disabled)

Callbacks and Transient Attributes

Use these for complex setup scenarios.

Steps to implement:

Create a user with ebooks using transient attributes:

factory :user do
  name { Faker::Name.name }
  email { Faker::Internet.unique.email }

  transient do
    ebooks_count { 0 }
  end

  after(:create) do |user, evaluator|
    create_list(:ebook, evaluator.ebooks_count, seller: user)
  end
end

Use in tests:

seller = create(:user, ebooks_count: 5)
expect(seller.ebooks.count).to eq(5)

Create ebook with purchases:

factory :ebook do
  # ... other attributes ...

  transient do
    purchases_count { 0 }
  end

  after(:create) do |ebook, evaluator|
    create_list(:purchase, evaluator.purchases_count, ebook: ebook)
  end
end

Exercise

Apply these concepts to your ebook application:

Create factories for all your models:
User factory with Faker for name and email
Ebook factory with Faker for title, description, and price
Purchase factory with proper associations
Tag factory (if you implemented the tags system)
Add traits to your factories:
Ebook: :draft, :pending, :published, :with_pdf
User: :enabled, :disabled, :seller_with_ebooks
Create complex factories with transient attributes:
User with N ebooks: create(:user, ebooks_count: 10)
Ebook with N purchases: create(:ebook, :published, purchases_count: 5)
Refactor existing tests:
Replace all manual User.create and Ebook.create with factories
Use traits to simplify test setup
Use build instead of create when you don't need database persistence