gistfile1.rb

# Implementation
class PostsController < ApplicationController
  def index
    @posts = Post.published
  end

  def new
    @post = Post.new
  end

  def create
    @post = Post.new(params[:post])
    @post.save
    flash[:success] = 'Post created.'
    redirect_to posts_path
  end
end

# Functional (component) test
require 'test_helper'

class PostsControllerTest < ActionController::TestCase
  context 'GET to index' do
    setup do
      Factory(:unpublished_post)
      @published_posts = [Factory(:published_post), Factory(:published_post)]
      get :index
    end

    should_render_template :index
    should_respond_with    :success
    should_assign_to       :posts

    should "find all the published posts" do
      assert_equal @published_posts, assigns(:posts)
    end
  end

  context 'POST to create with valid parameters' do
    setup do
      @posts_count = Post.count
      @post_attributes = Factory.attributes_for(:post)
      post :create, :post => @post_attributes
    end

    should_set_the_flash_to /created/i
    should_redirect_to('posts index') { posts_path }

    should "create a post" do
      assert_equal @posts_count + 1, Post.count
    end

    should "create a Post with the specified attributes" do
      created_post = Post.last
      @post_attributes.each do |attribute, value|
        assert_equal value, created_post[attribute]
      end
    end
  end
end

# Isolation test
require 'test_helper'

class PostsControllerTest < ActionController::TestCase
  context 'GET to index' do
    setup do
      @published_posts = [Factory.stub(:post)]
      Post.stubs(:published).returns(@published_posts)
      get :index
    end

    should_render_template :index
    should_respond_with    :success
    should_assign_to       :posts

    should "find all the published posts" do
      assert_received(Post, :published)
    end

    should "pass the published posts into the view" do
      assert_equal @published_posts, assigns(:posts)
    end
  end

  context 'POST to create with valid parameters' do
    setup do
      @post_attributes = {}
      @post = stub('post', :save => true)
      Post.stubs(:new).returns(@post)
      post :create, :post => @post_attributes
    end

    should_set_the_flash_to /created/i
    should_redirect_to('posts index') { posts_path }

    should "instantiate a Post with the specified attributes" do
      assert_received(Post, :new) { |expect| expect.with(@post_attributes) }
    end

    should "save the Post" do
      assert_received(@post, :save)
    end
  end
end