user_create.rb

class UserCreate
  def initialize(params)
    @params = params
  end
  attr_reader :params

  def user
    @user ||= User.new(params[:user])
  end

  def create
    add_address
    user.save
  end

  private

  def add_address
    @user.build_address(params[:address])
  end
end

user_create_integration_spec.rb

# requirement in the user_create.rb. Not inside to this example
require 'user'
require 'address'
##

#require 'user_create'
require 'spec_helper' # All rails stack

describe UserCreate, "integrations" do

  let(:user_create) { UserCreate.new({:user => {'name' => 'Cyril'}, :address => {'num' => 46}}) }

  describe "#user" do
    it 'initialize a user with params pass in args' do
      expect(user_create.user).to be_a(User)
      expect(user_create.user.name).to eq 'Cyril'
    end

    it 'memoize the user initialize' do
      expect(user_create.user).to eq user_create.user
    end
  end

  describe "#save" do

    it 'save the user' do
      expect {
        user_create.save
      }.to change(User.count).by(1)
    end

    it 'add address' do
      expect {
        user_create.save
      }.to change(Address.count).by(1)
      expect(user_create.user.address).to be_a(Address)
      expect(user_create.user.address.num).to eq 46
    end
  end

end

user_create_with_stub_persistence_spec.rb

# requirement in the user_create.rb. Not inside to this example
require 'user'
require 'address'
##

require 'user_create'

describe UserCreate, "without DB connection" do

  let(:user_create) { UserCreate.new({:user => {'name' => 'Cyril'}, :address => {'num' => 46}}) }

  describe "#user" do
    it 'initialize a user with params pass in args' do
      expect(user_create.user).to be_a(User)
      expect(user_create.user.name).to eq 'Cyril'
    end

    it 'memoize the user initialize' do
      expect(user_create.user).to eq user_create.user
    end
  end

  describe "#save" do
    before do
      user_create.user.should_receive(:save).and_return(true)
    end

    it 'save the user' do
      user_create.save
    end

    it 'add address' do
      user_create.save
      expect(user_create.user.address).to be_a(Address)
      expect(user_create.user.address.num).to eq 46
    end
  end

end

user_create_without_model_require_spec.rb

require 'user_create'

describe UserCreate, "without User model requirement" do

  before do
    User.stub(:new).with({'name' => 'Cyril'}).and_return(user)
  end
  let(:user_create) { UserCreate.new({:user => {'name' => 'Cyril'}, :address => {'num' => 46}}) }
  let(:user) {mock(:user, :save => true) }

  describe "#user" do
    it 'initialize a user with params pass in args' do
      expect(user_create.user).to be_a(User)
    end

    it 'memoize the user initialize' do
      expect(user_create.user).to eq user_create.user
    end
  end

  describe "#save" do
    it 'save the user' do
      user.should_receive(:save).and_return(true)
      user_create.save
    end

    it 'add address' do
      user.should_receive(:build_address).with({'num' => 46})
      user_create.save
    end
  end

end