如何测试我的控制器是否在Rails 3上呈现了正确的布局?

Controller code:

控制器代码:

class BooksController < ApplicationController
  def index
    @books = Book.all
    respond_to do |format|
      format.html do
        render 'index', :layout => 'topgun'
      end
    end
  end
end
class BooksControll