users_controller.rb

class Api::UsersController < ApplicationController

  def index
    @users = User.all
    render json: @users
  end

  def show
    @user = User.find params[:id]
    render json: @user
  end

  def create
    @user = User.new user_params

    if @user.save
      render json: @user, status: :created, location: api_user_url(@user)
    else
      render json: @user.errors, status: :unprocessable_entity
    end
  end

  def update
    @user = User.find params[:id]
    if @user.update user_params
      head :no_content
    else
      render json: @user.errors, status: :unprocessable_entity
    end
  end

  def destroy
    @user = User.find params[:id]
    @user.destroy
    head :no_content
  end
  
end

users_controller_spec.rb

require 'spec_helper'

describe Api::UsersController do

  render_views

  let(:user) { |build :user, id: 1 }

  context "index action should return 'OK'" do
    before do
      @users = (1..3).map { |n| build :user, id: n }
      User.expects(:all).returns(@users).once
      get :index
    end

    it { should assign_to(:users).with(@users) }
    it { should respond_with(:ok) }
  end

  context "show action should return 'OK'" do
    before do
      User.expects(:find).returns(user)
      get :show, id: user
    end

    it { should assign_to(:user).with(user) }
    it { should respond_with(:ok) }
  end

  context "create action is invalid" do
    before do
      User.any_instance.expects(:valid?).returns(false)
      User.any_instance.expects(:errors)
      post :create, user: attributes_for(:invalid_user)
    end

    it { should respond_with(:unprocessable_entity) }
  end

  context "create action is valid" do
    before do
      User.any_instance.expects(:valid?).returns(true)
      post :create, user: attributes_for(:user)
    end
    
    it { should assign_to(:user).with(user) }
    it { should respond_with(:created) }
  end

  context "update action is invalid" do
    before do
      User.expects(:find).returns(user)
      User.any_instance.expects(:valid?).returns(false)
      User.any_instance.expects(:errors)
      put :update, id: user, user: attributes_for(:invalid_user)
    end
    
    it { should respond_with(:unprocessable_entity) }
  end

  context "update action is valid" do
    before do
      User.expects(:find).returns(user)
      User.any_instance.expects(:valid?).returns(true)
      put :update, id: user, user: attributes_for(:user)
    end

    it { should respond_with(:no_content) }
  end

  context "destroy action" do
    before do
      User.expects(:find).returns(user)
      User.any_instance.expects(:destroy)
      delete :destroy, id: user
    end

    it { should respond_with(:no_content) }
  end

end