Refactor domain mailer

- Remove `Que::Mailer` (#895)
- Add preview
- DRY templates
- Add tests
- Extract translations

test/models/domain_cron_test.rb

@@ -0,0 +1,21 @@
+require 'test_helper'
+
+class DomainCronTest < ActiveSupport::TestCase
+  include ActionMailer::TestHelper
+
+  setup do
+    @domain = domains(:shop)
+    ActionMailer::Base.deliveries.clear
+  end
+
+  def test_clean_expired_pendings_notifies_registrant_by_email
+    Setting.expire_pending_confirmation = 0
+    @domain.update!(registrant_verification_asked_at: Time.zone.now,
+                    registrant_verification_token: 'test',
+                    statuses: [DomainStatus::PENDING_DELETE_CONFIRMATION])
+
+    DomainCron.clean_expired_pendings
+
+    assert_emails 1
+  end
+end