fixup! Extract FoiAttachment::Dsn & restore functionality

Add FoiAttachment#extra_note spec

spec/factories/foi_attchments.rb

@@ -61,6 +61,12 @@
       body { 'someimage' }
     end
 
+    factory :delivery_status_notification_attachment do
+      content_type { 'message/delivery-status' }
+      filename { 'attachment.delivery_status' }
+      body { load_file_fixture('attachment.delivery_status') }
+    end
+
     factory :unknown_attachment do
       content_type { 'application/unknown' }
       filename { 'interesting.spc' }

spec/fixtures/files/attachment.delivery_status

@@ -0,0 +1,10 @@
+X-Symantec-Messaging-Gateway-Queue-ID: EE/CD-06721-9C109DE4
+X-Symantec-Messaging-Gateway-Sender: rfc822; [email protected]
+Reporting-MTA: dns; gov.example.com
+Arrival-Date: Sat, 03 Dec 2011 04:50:17 +0000
+
+Final-Recipient: rfc822; [email protected]
+Status: 4.4.0
+Action: delayed
+Last-Attempt-Date: Sat, 03 Dec 2011 04:50:17 +0000
+Diagnostic-Code: smtp; 421 4.4.0 [internal] no MXs for this domain could be reached at this time

spec/models/foi_attachment_spec.rb

@@ -374,4 +374,26 @@
       it { is_expected.to be_nil }
     end
   end
+
+  describe '#extra_note' do
+    subject { foi_attachment.extra_note }
+
+    context 'with a delivery status notification' do
+      let(:foi_attachment) do
+        FactoryBot.create(:delivery_status_notification_attachment)
+      end
+
+      let(:note) do
+        '<em>DSN: 4.4.0 Other or undefined network or routing status</em>'
+      end
+
+      it { is_expected.to eq(note) }
+      it { is_expected.to be_html_safe }
+    end
+
+    context 'with any other content type' do
+      let(:foi_attachment) { FactoryBot.build(:rtf_attachment) }
+      it { is_expected.to be_nil }
+    end
+  end
 end