Merge pull request #8141 from alphagov/ensure-document-slug-does-not-…

…change-once-published

Ensure document slug can never change once an edition has been published

app/models/document.rb

@@ -81,7 +81,7 @@ def should_generate_new_friendly_id?
   end
 
   def update_slug_if_possible(new_title)
-    return if live? || invalid?
+    return if ever_published_editions.present? || invalid?
 
     candidate_slug = normalize_friendly_id(new_title)
     unless candidate_slug == slug

test/unit/app/models/edition/identifiable_test.rb

@@ -132,6 +132,15 @@ class Edition::IdentifiableTest < ActiveSupport::TestCase
     assert_equal "this-is-my-publication", existing_edition.document.reload.slug
   end
 
+  test "should not update slug when after an edition has been unpublished" do
+    unpublished_edition = create(:superseded_publication, title: "This is my publication")
+    draft_edition = create(:draft_publication, title: "This is my publication", document: unpublished_edition.document)
+
+    draft_edition.title = "New title"
+    draft_edition.save!
+    assert_equal "this-is-my-publication", draft_edition.document.reload.slug
+  end
+
   test "updating an edition updates the parent document timestamp" do
     edition = create(:edition)