rspec 模拟某些对象时出现问题

Question

当我尝试删除某些方法时，我看到一些奇怪的行为。我正在使用 Rails 3.0.3 和 rspec 2.3.0

这是规范文件的相关部分

    require 'spec_helper'
    include Authlogic::TestCase

    describe PrizesController do

      before do
        activate_authlogic
        @manager = Factory.create(:valid_manager, :name => "Test Manager ")
        UserSession.create @manager
      end

      def mock_prize(stubs={})
        (@mock_prize ||= mock_model(Prize, :point_cost => 100).as_null_object).tap do |prize|
          prize.stub(stubs) unless stubs.empty?
        end
      end

      def mock_consumable(stubs={})
        (@mock_consumable ||= mock_model(Consumable).as_null_object).tap do |consumable|
          consumable.stub(stubs) unless stubs.empty?
        end

  end

  describe "GET buy_this" do
    it "assigns the requested prize as @prize and requested consumable as @consumable if the player has enough points" do
      Prize.stub(:find).with("37") { mock_prize }
      @manager.should_receive(:available_points).and_return(1000)
      get :buy_this, :id => "37", :user_id => @manager.id
      assigns(:prize).point_cost.should eq(100)
      assigns(:prize).should be(mock_prize) 
      assigns(:consumable).should_not be_nil 
    end 

    it "assigns the requested prize as @prize and no consumable as @consumable if the player does not have enough points" do
      Prize.stub(:find).with("37") { mock_prize }
      @manager.should_receive(:available_points).and_return(10)
      get :buy_this, :id => "37", :user_id => @manager.id
      assigns(:prize).point_cost.should eq(100)
      assigns(:prize).should be(mock_prize)
      assigns(:consumable).should be_nil
    end
  end

和控制器方法：

 def buy_this
    @prize = Prize.find(params[:id])
    user = User.find(params[:user_id]) if params[:user_id]
    user ||= current_user
    flash[:notice] = ("Attempting to redeem points for a prize")
    if user.available_points > @prize.point_cost
      @consumable = user.consumables.create(:kind => @prize.consumable_kind, :description => @prize.consumable_description, :redemption_message => @prize.consumable_redemption_message)
      point_record = @consumable.create_point_record(:redeemed_points => @prize.point_cost)
      point_record.user = user
      point_record.save
      flash[:success] = "You successfully redeemed #{@prize.point_cost} points for #{@prize.name}"
    else
      flash[:error] = "Sorry, you don't seem to have enough points to buy this"
    end
    redirect_to prizes_path
  end

测试失败，这是输出...

  1) PrizesController GET buy_this assigns the requested prize as @prize and requested consumable as @consumable if the player has enough points
     Failure/Error: assigns(:consumable).should_not be_nil
     expected not nil, got nil
     # ./spec/controllers/prizes_controller_spec.rb:39

  2) PrizesController GET buy_this assigns the requested prize as @prize and no consumable as @consumable if the player does not have enough points
     Failure/Error: @manager.should_receive(:available_points).and_return(10)
     (#<User:0x10706b000>).available_points(any args)
         expected: 1 time
         received: 0 times
     # ./spec/controllers/prizes_controller_spec.rb:44

对此有什么想法吗？我完全困惑为什么使用相同参数调用相同方法的两个测试会以不同的方式失败（更不用说，我根本不明白为什么它们会失败......）。