如何在Ruby on Rails中使用FactoryGirl嵌套屬性創建測試對象？

我有一個Invoice模型可能包含許多Items還有：如何在Ruby on Rails中使用FactoryGirl嵌套屬性創建測試對象？

class Invoice < ActiveRecord::Base 

    attr_accessible :number, :date, :recipient, :items_attributes 

    belongs_to :user 

    has_many :items 

    accepts_nested_attributes_for :items, :reject_if => :all_blank, :allow_destroy => true 

end

我想對此進行測試使用RSpec的：

describe InvoicesController do 

    describe 'user access' do 

    before :each do 
     @user = FactoryGirl.create(:user) 
     @invoice = @user.invoices.create(FactoryGirl.attributes_for(:invoice)) 
     sign_in(@user) 
    end 

    it "renders the :show view" do 
     get :show 
     expect(response).to render_template :show 
    end 

    end 

end

不幸的是，這個測試（和所有其他人）失敗並顯示RSpec的此錯誤消息：

Failure/Error: @invoice = @user.invoices.create(FactoryGirl.attributes_for(:invoice)) 
ActiveModel::MassAssignmentSecurity::Error: 
Can't mass-assign protected attributes: items

如何創建一個可通過我的測試的項目的發票？

我使用FactoryGirl製造這樣的對象：

factory :invoice do 
    number { Random.new.rand(0..1000000) } 
    recipient { Faker::Name.name } 
    date { Time.now.to_date } 
    association :user 
    items { |i| [i.association(:item)] } 
end 

factory :item do 
    date { Time.now.to_date } 
    description { Faker::Lorem.sentences(1) } 
    price 50 
    quantity 2 
end

來源

2013-03-04 Tintin81