问Rails自定义在控制器测试中不注册sign_in用户

EN

require 'spec_helper'

describe EngagementsController do
  describe "GET show" do
    let(:user) { FactoryGirl.create(:user) }
    before { sign_in user }

    it "assigns requested engagement to @engagement" do
      engagement = FactoryGirl.create(:engagement, user: user)
      get :show, id: engagement
      assigns[:engagement].should eq(engagement)
    end

    it "renders :show" do
      engagement = FactoryGirl.create(:engagement, user: user)
      get :show, :id => engagement.id
      expect(response).to render_template("show")
    end
  end
end

 EngagementsController GET show renders :show
 Failure/Error: expect(response).to render_template("show")
   expecting <"show"> but rendering with <[]>
 # ./spec/controllers/engagements_controller_spec.rb:37:in `block (3 levels) in < top (required)>'

 EngagementsController GET show assigns requested engagement to @engagement
 Failure/Error: assigns[:engagement].should eq(engagement)  
 expected: #<Engagement id: 42, title: "Coding", content: "Got in the zone with coding", user_id: 46, created_at: "2014-08-28 21:08:43", updated_at: "2014-08-28 21:08:43", photo_file_name: nil, photo_content_type: nil, photo_file_size: nil, photo_updated_at: nil>
        got: nil
   (compared using ==)
 # ./spec/controllers/engagements_controller_spec.rb:31:in `block (3 levels) in < top (required)>'

class EngagementsController < ApplicationController
  before_action :signed_in_user
  before_action :correct_user, only: [:show]

  def show
    @engagement = Engagement.find(params[:id])
  end

  private

  def correct_user
    @engagement = current_user.engagements.find_by_id(params[:id])
    if @engagement.nil? && !current_user.try(:admin)
      redirect_to root_url
    end
  end