FactoryBot: Associations, Callbacks & Best Practices

Associations

factory :post do
  title { "My Post" }
  association :author, factory: :user
end

# Creating a :post automatically creates the related :user too,
# mirroring the model's actual belongs_to association

Watching Association Overhead

If every test creating a Post also creates a full User (and that User's own associations), the cumulative database writes across hundreds of tests can meaningfully slow the suite down -- worth being deliberate about which associations actually auto-create.

Callbacks

factory :user do
  name { "Ada" }

  after(:create) do |user|
    create(:profile, user: user)
  end
end

# Runs additional setup once the base object is actually created --
# useful for coordinated multi-object setup

Factory Inheritance

factory :admin_user, parent: :user do
  role { "admin" }
end

# Cleanly layers on top of :user's defaults instead of
# cramming conditional logic into one large factory

Pairing With Faker

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

# Varied, realistic random data can surface edge cases that
# a single hardcoded test value would never reveal