Added ability to create topic sorts in plugins with custom_fields

spec/components/topic_query_spec.rb

@@ -232,6 +232,33 @@ describe TopicQuery do
 
           # returns the topics in reverse posters order if requested" do
           expect(ids_in_order('posters', false)).to eq([archived_topic, closed_topic, invisible_topic, future_topic, regular_topic, pinned_topic].map(&:id))
+    
+          # sets a custom field for each topic to emulate a plugin
+          regular_topic.custom_fields["sheep"] = 26
+          pinned_topic.custom_fields["sheep"] = 47
+          archived_topic.custom_fields["sheep"] = 69
+          invisible_topic.custom_fields["sheep"] = 12
+          closed_topic.custom_fields["sheep"] = 31
+          future_topic.custom_fields["sheep"] = 53
+          
+          regular_topic.save
+          pinned_topic.save
+          archived_topic.save
+          invisible_topic.save
+          closed_topic.save
+          future_topic.save
+
+          # adds the custom field as a viable sort option
+          class ::TopicQuery
+            SORTABLE_MAPPING["sheep"] = "custom_fields.sheep"
+          end
+          # returns the topics in the sheep order if requested" do
+          expect(ids_in_order('sheep')).to eq([archived_topic, future_topic, pinned_topic, closed_topic, regular_topic, invisible_topic].map(&:id))
+
+          # returns the topics in reverse sheep order if requested" do
+          expect(ids_in_order('sheep', false)).to eq([invisible_topic, regular_topic, closed_topic, pinned_topic, future_topic, archived_topic].map(&:id))
+    
+
         end
 
       end