Issue testing create action with invalid parameters when using respond_to/respond_with in Rails 3.x

testing-invalid-params-with-respond_with

# Issue testing create action with invalid parameters when using respond_to/respond_with in Rails 3.x

When a new "thing" is saved without invalid params, the respond_with behavior is to render :new again. 
But since the form has been submitted to :root/things/, what actually displays in the browser is http://:root/things and not http://:root/things/new. 
Somehow this confuses the render_template test in RSpec and it believes the current template is "" instead of "new", which results in a failed test.

The only solution I found was to write the create action like this:

    if @thing.save 
      respond_with @thing 
    else 
      render :new 
    end

But that kind of defeats the purpose of the respond_with elegance, doesn't it?
I'd love to hear feedback on this. I'm still new to Rails and especially new to testing.

You can find all the details below.

## Model

class Thing < ActiveRecord::Base
  ### schema
  # name      string
  # store_id  integer
  ###

  has_and_belongs_to_many :stores
  attr_accessible :name
  validates :name, presence: true
end

## Controller

class ThingController < ApplicationController
  respond_to :html, :json
  
  (...)

  def new
    @thing = Thing.new
    respond_with @thing
  end

  def create
    @thing = Device.new(params[:thing])
    @thing.save 
    respond_with @thing
  end

  (...)

## RSpec Controller test

describe ThingController do
  describe "POST create" do
    describe "with invalid params" do
      it "assigns a newly created but unsaved device as @thing" do
        Thing.any_instance.stub(:save).and_return(false)
        post :create, :thing => {}
        assigns(:thing).should be_a_new(Thing)
      end

      it "re-renders the 'new' template" do
        Thing.any_instance.stub(:save).and_return(false)
        post :create, :thing => {}
        response.should render_template("new")
      end
    end
  end

## RSpec result

Failures:

  1) ThingsController POST create with invalid params re-renders the 'new' template
     Failure/Error: response.should render_template("new")
       expecting <"new"> but rendering with <"">
     # ./spec/controllers/things_controller_spec.rb:93:in `block (4 levels) in <top (required)>'

Finished in 0.78002 seconds
9 examples, 1 failure

## Log output

Started POST "/en/things" for 127.0.0.1 at 2011-08-17 09:35:38 -0400
  Processing by ThingsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"7J/MfJ/BHqVhIT4SCGlIYVy0lv+lpfkrHU63gFKZhUQ=", "thing"=>{"name"=>""}, "commit"=>"Save", "locale"=>"en"}
Rendered devices/_form.html.haml (4.5ms)
Rendered devices/new.html.haml within layouts/application (6.0ms)
  User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
   (0.2ms)  SELECT COUNT(*) FROM "stores" WHERE "stores"."user_id" = 1
Completed 200 OK in 248ms (Views: 235.8ms | ActiveRecord: 1.7ms)

## Visual result

http://link.olivierlacan.com/9NRg

Having the same issue, news on this?

be_redirect works, but in logs you see how it doesn't redirect.

http://stackoverflow.com/questions/13462123/rspec-test-on-response-should-be-successful-fails