UX: Don't highlight the latest poster in the topic list if there is only

one avatar shown.

app/models/topic_posters_summary.rb

@@ -16,7 +16,7 @@ class TopicPostersSummary
     TopicPoster.new.tap do |topic_poster|
       topic_poster.user = user
       topic_poster.description = descriptions_for(user)
-      topic_poster.extras = 'latest' if is_latest_poster?(user)
+      topic_poster.extras = 'latest' if include_latest_class?(user)
     end
   end
 
@@ -29,6 +29,10 @@ class TopicPostersSummary
     end
   end
 
+  def include_latest_class?(user)
+    topic.last_post_user_id == user.id && user_ids.uniq.size > 1
+  end
+
   def descriptions_for(user)
     descriptions_by_id[user.id].join ', '
   end
@@ -56,10 +60,6 @@ class TopicPostersSummary
     topic.user_id == topic.last_post_user_id
   end
 
-  def is_latest_poster?(user)
-    topic.last_post_user_id == user.id
-  end
-
   def sorted_top_posters
     shuffle_last_poster_to_back_in top_posters
   end

spec/models/topic_posters_summary_spec.rb

@@ -27,7 +27,6 @@ describe TopicPostersSummary do
 
       summary.first.tap do |topic_poster|
         expect(topic_poster.user).to eq topic_creator
-        expect(topic_poster.extras).to eq 'latest'
         expect(topic_poster.description).to eq(
           "#{I18n.t(:original_poster)}, #{I18n.t(:most_recent_poster)}"
         )
@@ -65,6 +64,8 @@ describe TopicPostersSummary do
           featured_user1, featured_user2, featured_user3,
           last_poster
         ])
+        # If more than one user, attach the latest class
+        expect(summary.last.extras).to eq 'latest'
       end
     end
   end