控制器规范#显示操作:exected:[Object],得到:nil错误-RSpec 3

我正在阅读Aaron Sumner的《RSpec日常轨道测试》(3)一书,无法通过以下步骤:

我正试图找出一个 users#show 操作:

用户_控制器规范:

...    
describe 'GET #show' do

  it "assigns the requested contact to @user" do
    user = create(:user)
    get :show, id: user.id
    expect(assigns(:user)).to eq user
  end


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

end
...

用户_控制器:

class UsersController < ApplicationController
  before_action :authenticate
  before_action :set_user, only: [:show]

  ### Read:
  def show
    ...
  end


  private

  def set_user
    @user = User.find(params[:id])
  end

end

application_controller助手:

  def authenticate
    redirect_to home_path, alert: 'Please log in first' if current_user.nil?
  end

  private 

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  helper_method :current_user

错误:

Failures:

  1) UsersController GET #show assigns the requested user to @user
     Failure/Error: expect(assigns(:user)).to eq user

       expected: #<User id: 1, ...">
            got: nil

       (compared using ==)
     # ./spec/controllers/users_controller_spec.rb:10:in `block (3 levels) in <top (required)>'

  2) UsersController GET #show renders the :show template
     Failure/Error: expect(response).to render_template :show
       expecting <"show"> but rendering with <[]>
     # ./spec/controllers/users_controller_spec.rb:17:in `block (3 levels) in <top (required)>'