ruby-on-rails – Rspec未定义方法’应该收到’

undefined method `should_receive' for ShortenedUrl:Class

这是我的spec_helper.rb文件：

# This file is copied to spec/ when you run 'rails generate rspec:install'
ENV["RAILS_ENV"] ||= 'test'
require File.expand_path("../../config/environment",__FILE__)
require 'rspec/rails'

# Requires supporting ruby files with custom matchers and macros,etc,# in spec/support/ and its subdirectories.
Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}

RSpec.configure do |config|
  # == Mock Framework
  #
  # If you prefer to use mocha,flexmock or RR,uncomment the appropriate line:
  #
  # config.mock_with :mocha
  # config.mock_with :flexmock
  # config.mock_with :rr
  config.mock_with :rspec

  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
  # config.fixture_path = "#{::Rails.root}/spec/fixtures"

  # If you're not using ActiveRecord,or you'd prefer not to run each of your
  # examples within a transaction,remove the following line or assign false
  # instead of true.
  # config.use_transactional_fixtures = true

  config.before(:each) do
    Mongoid.master.collections.each(&:drop)
  end
end

这是我的测试文件：

require 'spec_helper'

describe UrlsController do

  describe "POST make_short" do

    context "when posting a valid url" do
      # url = mock('ShortenedUrl')
      url = Struct.new('ShortenedUrl')
      ShortenedUrl.should_receive(:new).with(:url => 'http://example.com').and_return(url)
      url.should_receive(:save!)

      post :make_short,:url => 'http://example.com'
    end

  end

end

最后,这是Gemfile：

source 'http://rubygems.org'

gem 'rails','3.0.3'
gem "mongoid",">= 2.0.0.beta.19"
gem "rspec-rails",">= 2.0.1",:group => [:development,:test]
gem "cucumber-rails",:group => :test
gem "capybara",:group => :test

根据我的理解,如果我没有使用rspec模拟,我应该得到这个错误,但在我的情况下,我正在使用它.有任何想法吗？