FIX: Avoid publishing a gigantic payload.

* Certain sites have way too many categories.

spec/models/group_spec.rb

@@ -539,6 +539,20 @@ describe Group do
         expect(message.data[:categories].first[:id]).to eq(category.id)
         expect(message.user_ids).to eq([user.id])
       end
+
+      describe "when group belongs to more than #{Group::PUBLISH_CATEGORIES_LIMIT} categories" do
+        it "should publish a message to refresh the user's client" do
+          (Group::PUBLISH_CATEGORIES_LIMIT + 1).times do
+            group.categories << Fabricate(:category)
+          end
+
+          message = MessageBus.track_publish { group.add(user) }.first
+
+          expect(message.data).to eq('clobber')
+          expect(message.channel).to eq('/refresh_client')
+          expect(message.user_ids).to eq([user.id])
+        end
+      end
     end
   end