Possible approach to a hexagonal gem with rspec test

create_customer.rb

module HexagonalGem
  class CreateCustomer
    attr_reader :listener, :validator

    def self.create customer, listener = {}
      c = CreateCustomer.new(listener)
      c.create(customer)
    end

    def initialize(listener)
      @listener = listener
    end

    def create(customer)
      HexagonalGem.repository.insert(customer)

      @listener.created_customer(customer)
    end
  end
end

create_customer_spec.rb

require 'spec_helper'

describe HexagonalGem::CreateCustomer do
  let(:listener) { double('listener') }
  let(:repo) { HexagonalGem.repository }

  subject(:create_customer) { HexagonalGem::CreateCustomer.new(listener) }

  context 'with valid data' do
    let(:customer) { {email: '[email protected]'} }

    it 'callbacks with success' do
      listener.should_receive('created_customer')
      create_customer.create(customer)
    end

    it 'saves to repo' do
      listener.should_receive('created_customer')
      expect{create_customer.create(customer)}.to change{repo.count}.from(0).to(1)
    end
  end
end