controller_spec.rb

# Controller /app/controllers/posts_controller.rb
def index
  @posts = Post.all
end

# Spec /spec/controllers/posts_controller_spec.rb
describe "GET #index" do
  it "responds successfully with a HTTP 200 status code" do
    get :index
    expect(response).to be_success
    expect(response).to have_http_status(200)
  end

  it "should render index template" do
    get :index
    expect(response).to render_template('index')
  end
end

# Controller /app/controllers/posts_controller.rb
def create
  @post = Post.new post_params

  respond_to do |format|
    if @post.save
      format.html { redirect_to @post }
    else
      format.html { render action: :new }
    end
  end
end

# Spec /spec/controllers/posts_controller_spec.rb
describe "POST #create" do
  it "should create new post with valid params" do
    post :create, post: { title: 'My First Post', description: 'My first post description' }
    expect(Post.count).to eq(1)
  end

  it "redirects to show page once the post is created successfully" do
    post :create, post: { title: 'My First Post', description: 'My first post description' }
    expect(response).to redirect_to(Post.first)
  end

  it "does not allow to create post without title" do
    post :create, post: { description: 'My first post description' }
    expect(Post.count).to eq(0) # This make sure validates :title, presence: true in post.rb
  end

  it "renders new template if failed to create post" do
    post :create, post: { description: 'My first post description' }
    expect(response).to render_template('new')
  end
end

# Controller /app/controllers/posts_controller.rb
def update
  @post = Post.find params[:id]

  respond_to do |format|
    if @post.update_attributes(post_params)
      format.html { redirect_to @post }
    else
      format.html { render action: :edit }
    end
  end
end

# Spec /spec/controllers/posts_controller_spec.rb
describe "PUT update/:id" do
  before(:each) do
    @post = FactoryGirl.create(:post)
  end

  it "should render edit template if unable to create post" do
    @attr = { title: nil, description: 'My first post description' }
    put :update, id: @post.id, post: @attr

    expect(response).to render_template('edit')
  end

  it "redirects user on show post page" do
    @attr = { title: 'My First Post', description: 'My first post description' }
    put :update, id: @post.id, post: @attr

    expect(response).to have_http_status(302)
    expect(response).to redirect_to(@post)
  end

  it "validates the title and description of post after updation" do
    @attr = { title: 'My 1st Post', description: 'My 1st post description updated' }
    put :update, id: @post.id, post: @attr
    @post.reload

    expect(@post.title).to eql(@attr[:title])
    expect(@post.description).to eql(@attr[:description])
  end
end