feat(mail): devise confirmation instructions respect user preferred host

spec/mailers/devise_user_mailer_spec.rb

@@ -16,8 +16,37 @@ RSpec.describe DeviseUserMailer, type: :mailer do
 
     context 'when perform_later is called' do
       it 'enqueues email in default queue for high priority delivery' do
-  expect { subject.deliver_later }.to have_enqueued_job.on_queue(Rails.application.config.action_mailer.deliver_later_queue_name)
-end
+        expect { subject.deliver_later }.to have_enqueued_job.on_queue(Rails.application.config.action_mailer.deliver_later_queue_name)
+      end
     end
   end
+
+  describe 'headers for user' do
+    context "confirmation email" do
+      subject { described_class.confirmation_instructions(user, token, opts = {}) }
+
+      context "legacy domain" do
+        it "respect preferred domain" do
+          expect(header_value("From", subject.message)).to eq(NO_REPLY_EMAIL)
+          expect(header_value("Reply-To", subject.message)).to eq(NO_REPLY_EMAIL)
+          expect(subject.message.to_s).to include("#{ENV.fetch("APP_HOST_LEGACY")}/users/confirmation")
+        end
+      end
+
+      context "new domain" do
+        let(:user) { create(:user, preferred_domain: :demarches_gouv_fr) }
+
+        it "respect preferred domain" do
+          expect(header_value("From", subject.message)).to eq("Ne pas répondre <ne-pas-repondre@demarches.gouv.fr>")
+          expect(header_value("Reply-To", subject.message)).to eq("Ne pas répondre <ne-pas-repondre@demarches.gouv.fr>")
+          expect(subject.message.to_s).to include("#{ENV.fetch("APP_HOST")}/users/confirmation")
+          expect(subject.message.to_s).to include("//#{ENV.fetch("APP_HOST")}/assets/mailer/republique")
+        end
+      end
+    end
+  end
+
+  def header_value(name, message)
+    message.header.fields.find { _1.name == name }.value
+  end
 end