Refactor registrant change mailer

#480

spec/jobs/domain_update_confirm_job_spec.rb

@@ -0,0 +1,18 @@
+require 'rails_helper'
+
+RSpec.describe DomainUpdateConfirmJob do
+  let(:domain) { instance_spy(Epp::Domain, registrant: registrant, errors: []) }
+  let(:registrant) { instance_double(Registrant) }
+  let(:registrant_change) { instance_spy(RegistrantChange) }
+
+  it 'confirms registrant change' do
+    expect(Epp::Domain).to receive(:find).and_return(domain)
+    expect(RegistrantChange).to receive(:new)
+                                    .with(domain: domain, old_registrant: registrant)
+                                    .and_return(registrant_change)
+
+    described_class.enqueue(domain_id = nil, action = RegistrantVerification::CONFIRMED)
+
+    expect(registrant_change).to have_received(:confirm)
+  end
+end