ruby-on-rails – 如何测试我的控制器是否在Rails 3上呈现正确的

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

如何在规范中测试？

require 'spec_helper'

describe BooksController do
  describe "GET index" do
    it "renders the topgun layout" do
      get :index
      # ???
    end
  end
end

我检查了this related post,但我的响应对象似乎没有布局属性/方法.