factory_bot_attributes_for.rb

require "bundler/inline"

gemfile true do
  git_source(:github) { "https://github.com/#{_1}.git" }
  source "https://rubygems.org"
  gem "factory_bot", "~> 6.0"
  gem "activerecord"
  gem "sqlite3"
end

require "active_record"
require "factory_bot"
require "minitest/autorun"
require "logger"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.string :title
    t.string :body
  end
end

class Post < ActiveRecord::Base; end

FactoryBot.define do
  NIL_TITLE = Object.new # sentinel values to differentiate explicit nils from implicit nils
  NIL_BODY  = Object.new

  factory :post do
    initialize_with { new(**attributes.reject { _2 in NIL_TITLE | NIL_BODY }) } # reject sentinels when initializing

    title { NIL_TITLE }
    body  { NIL_BODY }
  end
end

class FactoryBotTest < Minitest::Test
  def test_create
    post = FactoryBot.create(:post)

    assert_nil post.title
  end

  def test_build
    post = FactoryBot.build(:post)

    assert_nil post.title
  end

  def test_attributes_for
    post = FactoryBot.attributes_for(:post)

    assert_nil post[:title]
  end
end