Show correct last successful update timestamp

We were previously showing the `last_update_at` of pull mirror as
`Last successful update` timestamp. But that attribute gets set
whenever the mirror finished regardless if it failed or not.

We have the `last_successful_update_at` attribute that gets set
when the mirror successfully updated. This change uses that
attribute instead.

ee/app/views/projects/mirrors/_table_pull_row.html.haml

@@ -11,7 +11,7 @@
   %td= _('Pull')
   %td
     = import_state.last_update_started_at.present? ? time_ago_with_tooltip(import_state.last_update_started_at) : _('Never')
-  %td{ data: { qa_selector: 'mirror_last_update_at_cell' } }= import_state.last_update_at.present? ? time_ago_with_tooltip(import_state.last_update_at) : _('Never')
+  %td{ data: { qa_selector: 'mirror_last_update_at_cell' } }= import_state.last_successful_update_at.present? ? time_ago_with_tooltip(import_state.last_successful_update_at) : _('Never')
   %td
     - if import_state&.last_error.present?
       .badge.badge-danger{ data: { toggle: 'tooltip', html: 'true' }, title: html_escape(import_state.last_error.try(:strip)) }= _('Error')

ee/changelogs/unreleased/216535-show-accurate-last-successful-update.yml

+---
+title: Show correct last successful update timestamp
+merge_request: 32078
+author:
+type: fixed

ee/spec/features/projects/mirror_spec.rb

@@ -15,6 +15,34 @@ describe 'Project mirror', :js do
       sign_in user
     end
 
+    context 'when mirror was updated successfully' do
+      before do
+        import_state.update(last_successful_update_at: 5.minutes.ago)
+      end
+
+      it 'shows the last successful at timestamp' do
+        visit project_mirror_path(project)
+
+        page.within('.js-mirrors-table-body tr:nth-child(1) td:nth-child(4)') do
+          expect(page).to have_content('5 minutes ago')
+        end
+      end
+    end
+
+    context 'when mirror was never updated successfully' do
+      before do
+        import_state.update(last_successful_update_at: nil)
+      end
+
+      it 'shows that mirror has never been updated' do
+        visit project_mirror_path(project)
+
+        page.within('.js-mirrors-table-body tr:nth-child(1) td:nth-child(4)') do
+          expect(page).to have_content('Never')
+        end
+      end
+    end
+
     context 'with Update now button' do
       let(:timestamp) { Time.now }