stack overflow answer for 13093403

registrations_controller_spec.rb

require File.dirname(__FILE__) + '/../spec_helper'

describe Users::RegistrationsController do
  include Devise::TestHelpers
  fixtures :all
  render_views

  before(:each) do
    @request.env["devise.mapping"] = Devise.mappings[:user]
  end

  describe "POST 'create'" do
    describe "failure" do
      before(:each) do
        @attr = { :email => "", :password => "",
                  :password_confirmation => "", :display_name => "" }
      end

      it "should not create a user" do
        lambda do
          post :create, :user_registration => @attr
        end.should_not change(User, :count)
      end

      it "should render the 'new' page" do
        post :create, :user_registration => @attr
        response.should render_template('new')
      end
    end

    describe "success" do
      before(:each) do
        @attr = { :email => "user@example.com",
                  :password => "foobar01", :password_confirmation => "foobar01", :display_name => "New User" }
      end

      it "should create a user" do
        lambda do
          post :create, :user => @attr
          response.should redirect_to(root_path)
          #response.body.should have_selector('h1', :text => "Sample App")
          #response.should have_css('h1', :text => "Sample App")
          #flash[:success].should == "A message with a confirmation link has been sent to your email address. Please open the link to activate your account."
          #response.should have_content "A message with a confirmation link has been sent to your email address. Please open the link to activate your account."
        end.should change(User, :count).by(1)
      end

    end

  end

  describe "PUT 'update'" do
    before(:each) do
      @user = FactoryGirl.create(:user)
      @user.confirm! # or set a confirmed_at inside the factory. Only necessary if you are using the confirmable module
      sign_in @user
    end

    describe "Failure" do

      before(:each) do
        # The following information is valid except for display_name which is too long (max 20 characters)
        
        @attr = { :email => @user.email, :display_name => ("t" * 35), :current_password => @user.password }
      end

      it "should render the 'edit' page" do
        put :update, :id => subject.current_user, :user => @attr

        # HAVE PUT THE DEBUGS THAT I'D LIKE TO GET WORKING FIRST
        # Would like to be able to debug and check I'm getting the error(s) I'm expecting
        #puts subject.current_user.errors.messages # doesn't show me the errors
        # Would like to be able to debug what html is being returned:
        #puts page.html # only return the first line of html

        # Would like to be able to determine that this test is failing for the right reasons
        response.body.should include "Display name is too long (maximum is 30 characters)"
        assigns[:user].errors[:display_name].should include "is too long (maximum is 30 characters)"


        response.should render_template('edit')
      end
    end

    describe "Success" do

      it "should change the user's display name" do
        @attr = { :email => @user.email, :display_name => "Test", :current_password => @user.password }
        put :update, :id => subject.current_user, :user => @attr
        subject.current_user.reload
        response.should redirect_to(root_path)
        subject.current_user.display_name == @attr[:display_name]
      end

    end
  end

  describe "authentication of edit/update pages" do

    describe "for non-signed-in users" do

      before(:each) do
        @user = FactoryGirl.create(:user)
      end

      describe "for non-signed-in users" do

        it "should deny access to 'edit'" do
          get :edit, :id => @user
          response.should redirect_to(new_user_session_path)
        end

        it "should deny access to 'update'" do
          put :update, :id => @user, :user => {}
          response.should redirect_to(new_user_session_path)
        end

      end

    end
  end

end

schema.rb

# encoding: UTF-8
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your
# database schema. If you need to create the application database on another
# system, you should be using db:schema:load, not running all the migrations
# from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended to check this file into your version control system.

ActiveRecord::Schema.define(:version => 20121027180617) do

  create_table "users", :force => true do |t|
    t.string   "email",                  :default => "", :null => false
    t.string   "encrypted_password",     :default => "", :null => false
    t.string   "display_name"
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          :default => 0
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.string   "confirmation_token"
    t.datetime "confirmed_at"
    t.datetime "confirmation_sent_at"
    t.string   "unconfirmed_email"
    t.datetime "created_at",                             :null => false
    t.datetime "updated_at",                             :null => false
  end

  add_index "users", ["email"], :name => "index_users_on_email", :unique => true
  add_index "users", ["reset_password_token"], :name => "index_users_on_reset_password_token", :unique => true

end

user.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable, :confirmable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me, :display_name
  validates_length_of :display_name, maximum: 30
end

users:regsitrations_controller.rb

class Users::RegistrationsController < Devise::RegistrationsController
end