Dependency Injection example in Ruby

service.rb

require 'resolv'

class ConferenceDomainsService
  def initialize(conference, resolver = Resolv::DNS.new)
    @conference = conference
    @resolver = resolver
  end

  ##
  # Checks if domain correctly points to the hosted version
  # This feature is enabled only if ENV['OSEM_HOSTNAME'] is present
  #
  # ====Returns
  # * +true+ -> If the custom domain has a CNAME record for the hosted version
  # * +false+ -> If the custom domain does not have a CNAME record for the hosted version
  def check_custom_domain
    cname_record = @resolver.getresource(@conference.custom_domain, Resolv::DNS::Resource::IN::CNAME)
    cname_record.present? ? ENV['OSEM_HOSTNAME'] == cname_record.name.to_s : false
  end
end

service_spec.rb

require 'spec_helper'

describe ConferenceDomainsService do
  let(:conference) { create(:conference, custom_domain: 'demo.osem.io') }
  let(:resolver) { double('resolver') }
  let(:service) { ConferenceDomainsService.new(conference, resolver) }

  describe '#check_custom_domain' do
    subject { service.check_custom_domain }
    let(:cname_record) { double(name: cname_domain) }

    before do
      ENV['OSEM_HOSTNAME'] = 'osem-demo.herokuapp.com'
      allow(resolver).to receive(:getresources).with(conference.custom_domain, Resolv::DNS::Resource::IN::CNAME)
        .and_return(cname_record)
    end
    
    context 'when the cname record matches the domain name' do
      let(:cname_domain) { conference.custom_domain }
      it { is_expected.to eq true }
    end
    
    context 'when the cname record does not match the domain name' do
      let(:cname_domain) { 'random.domain.com' }
      it { is_expected.to eq false }
    end
    
    context 'when there is not cname record present' do
      let(:cname_record) { nil }
      it { is_expected.to eq false }
    end
  end
end