thoughtbot--factory_bot/spec/acceptance/attribute_aliases_spec.rb

describe "attribute aliases" do
  before do
    define_model('User', name: :string, age: :integer)

    define_model('Post', user_id: :integer) do
      belongs_to :user
    end

    FactoryBot.define do
      factory :user do
        factory :user_with_name do
          name { "John Doe" }
        end
      end

      factory :post do
        user
      end

      factory :post_with_named_user, class: Post do
        user factory: :user_with_name, age: 20
      end
    end
  end

  context "assigning an association by foreign key" do
    subject { FactoryBot.build(:post, user_id: 1) }

    it "doesn't assign both an association and its foreign key" do
      expect(subject.user_id).to eq 1
    end
  end

  context "assigning an association by passing factory" do
    subject { FactoryBot.create(:post_with_named_user).user }

    it "assigns attributes correctly" do
      expect(subject.name).to eq "John Doe"
      expect(subject.age).to eq 20
    end
  end
end