what's wrong with this?

wwwt.rb

class ItemImage < ActiveRecord::Base
  belongs_to :item, :polymorphic => true
  mount_uploader :image, ImageUploader
  scope :the_cover, where(:cover => true)
end

class Book < ActiveRecord::Base
  has_many :item_images, :as => :item
end

class Comicbook < ActiveRecord::Base
  has_many :item_images, :as => :item
end

context 'This book' do
    
    setup do
      @bookshop = Factory.create(:bookshop)
      @rare_book = Factory.create(:rare_book, :price => 50, :currency => 'EUR')
      @bookshop.items << @rare_book
    end

    should "have images" do 
      assert @rare_book.item_images.empty?
      @rare_book.item_images << Factory.create(:item_image, :cover => "1")
      @rare_book.save
      assert_equal true, @rare_book.item_images.first.cover
      assert !@rare_book.item_images.empty?
      assert !@rare_book.item_images.the_cover.empty?
    end

end