Service Objects in Ruby. Related video https://www.youtube.com/watch?v=Ydvu9gcu_iw

user_controller.rb

class UserController
  def create
    if params[:ads_source] == 'facebook'
      @user = UserCreator.build_for_fb(params)
    elsif params[:ads_source] == 'linkedin'
      @user = UserCreator.build_for_linkedin(params)
    else
      raise 'Invalid ad campaign'
    end
  end
end

user_controller_spec.rb

describe UserController do
  describe '#create' do
    let(:params) do
      {
        email: '[email protected]',
        first_name: 'Jan',
        last_name: 'Kowalski'
      }
    end

    it do
      ga_api = instance_double(GoogleAnalyticsAPI)
      expect(GoogleAnalyticsAPI).to receive(:new).and_return(ga_api)

      mixpanel_api = instance_double(MixpanelAPI)
      expect(MixpanelAPI).to receive(:new).and_return(mixpanel_api)

      user_creator = instance_double(UserCreator)
      expect(UserCreator).to receive(:new).with(ga_api, mixpanel_api).and_return(user_creator)

      user = double
      expect(user_creator).to receive(:call).with(params).and_return(user)

      post :create, params: params
    end
  end
end

user_creator.rb

class UserCreator
  def self.build_for_linkedin(params)
    new(LinkedInAPI.new).call(params)
  end

  def self.build_for_fb(params)
    new(FacebookAPI.new).call(params)
  end

  def initialize(stats_api)
    @stats_api = stats_api
  end

  def call(params)
    user = User.create(
      email: params[:email],
      name: full_name(params)
    )
    stats_api.send_event('user_created', params)
    user
  end

  private

  attr_reader :stats_api

  def full_name(params)
    params[:first_name] + params[:last_name]
  end
end