RSpec more examples

examples.rb

# ./spec/user_spec.rb

require_relative '../../lib/user.rb'
require 'ostruct'

RSpec.describe User do
  subject { described_class.new(name: name, payment_service: payment_service) }

  let(:name) { 'John Doe' }
  let(:success_result) { true }
  let(:payment_service) { class_double('PaymentProcessingService') }

  describe '#buy' do
    let(:item) { double(amount: 100) }

    before do
      allow(payment_service).to receive(:charge!).and_return(OpenStruct.new(successfull: success_result))
    end

    context 'when payment was succesfull' do
      let(:success_result) { true }

      it 'calls payment service with correct parameters' do
        expect(payment_service).to receive(:charge!).with(subject, item.amount).once

        subject.buy(item)
      end

      it 'successfully buyes an item' do
        expect { subject.buy(item) }.to change { subject.items.size }.by(1)
      end
    end

    context 'when payment was unsuccessfull' do
      let(:success_result) { false }

      it 'does not buy an item' do
        expect { subject.buy(item) }.to change { subject.items.size }.by(0)
      end
    end
  end
end

# ./payment_service.rb

class PaymentProcessingService
  class PaymentForbiddenError < StandardError; end

  class << self
    def charge!(user, amount)
      puts "Real API call"
    end
  end
end

# PaymentProcessingService.charge!(user, amount)
# => OpenStruct(successfull: true/false)


# ./user.rb

require_relative 'payment_processing_service.rb'

class User
  attr_reader :items, :payment_service

  def initialize(name:, payment_service:)
    @name = name
    @payment_service = payment_service
    @items = []
  end

  def buy(item)
    payment_result = payment_service.charge!(self, item.amount)
    @items << item if payment_result.successfull
  end
end