ruby-on-rails – NameError：未定义的局部变量或方法`app’

NameError: undefined local variable or method `app' for 
  #<RSpec::Core::ExampleGroup::Nested_1::Nested_1::Nested_1:0x00000004424880>

…

# spec/controllers/sessions_conroller_spec.rb
require 'spec_helper'

describe SessionsController do

  before do
    @user = User.gen!
  end

  describe "#create" do
    context "when sending valid email and password" do
      it "renders a json hash ..." do
        post :create,email: @user.email,password: @user.password
        expect(last_response.status).to eq(201)
      end
    end
  end

  describe "#destroy" do
    context "when sending valid email and authentication token" do
      it "renders a json hash ..." do
        delete :destroy,auth_token: @user.authentication_token
        expect(last_response.status).to eq(200)
      end
    end
  end

end

spec_helper.rb加载了一些混合.

ENV["RAILS_ENV"] ||= 'test'
require File.expand_path("../../config/environment",__FILE__)
require 'rspec/rails'
require 'rspec/autorun'
require 'capybara/rspec'
Dir[Rails.root.join("spec/support/**/*.rb")].each { |f| require f }

RSpec.configure do |config|
  config.include FactoryGirl::Syntax::Methods
  config.include Rack::Test::Methods,type: :controller
  config.fixture_path = "#{::Rails.root}/spec/fixtures"    
  config.use_transactional_fixtures = true
  config.infer_base_class_for_anonymous_controllers = false
  config.order = "random"
end