见了鬼了。@contest明明有值，还 respond_to save，下一条里就成 NilClass 了。是我对 Ruby 的理解有误么？

# coding: utf-8
class ContestsController < ApplicationController
  def create
    @contest = Contest.new(params[:contest])
    p '@contest supports save' if @contest.respond_to?(:save)
    if @contest.save
      flash[:notice] = '创建成功'
      redirect_to home_path
    else
      flash[:error] = '创建失败'
      render :action => :new
    end
  end
end

输出

Running: spec/controllers/contests_controller_spec.rb spec/models/contest_spec.rb
F"@contest supports save"
F*F

Pending:
  ContestsController POST create redirects to add mission page
    # Not yet implemented
    # ./spec/controllers/contests_controller_spec.rb:16

Failures:

  1) ContestsController POST create creates a contest
     Failure/Error: post :create, contest: { 'name' => contest.name }
     NoMethodError:
       undefined method `save' for nil:NilClass
     # ./app/controllers/contests_controller.rb:6:in `create'
     # ./spec/controllers/contests_controller_spec.rb:9:in `block (3 levels) in <top (required)>'

补上 spec

describe ContestsController do
  let(:my_contest) { FactoryGirl.create(:contest) }
  before(:each) { my_contest }
  describe 'POST create' do
    it 'creates a contest' do
      Contest.should_receive(:new).with(name: my_contest.name)
      post :create, contest: { name: my_contest.name }
    end
    it 'saves the contest' do
      Contest.stub(:new).and_return(my_contest)
      my_contest.should_receive(:save)
      post :create
    end
    it 'redirects to add mission page'
  end
end