Dependency Injection w/ Mocks

song_library_spec.rb

RSpec.describe SongService do
  require 'spec_helper'
  
  subject { SongService.new(gateway_service: gateway_service) }
  let(:song) { Song.new(name: 'Seek Up', artist: 'Dave Matthews Band', genre: 'Rock') }

  context 'create_song using mocks' do

    class MockSongGatewayService < SongGatewayService
      def create_song(song)
        song = song.clone
        song.id = 'abc'
        song.to_json
      end
    end

    let(:gateway_service) { MockSongGatewayService.new }

    it 'creates a valid song' do
      new_song = subject.create_song(song)
      expect(new_song.name).to eq song.name
      expect(new_song.artist).to eq song.artist
      expect(new_song.genre).to eq song.genre
      expect(new_song.id).to_not be_nil
      expect(new_song.id).to_not eq song.id
    end

    it 'raises a validation exception on required name field' do
      song.name = nil
      expect { subject.create_song(song) }.to raise_error
    end
  end
end