Should also stub the received callback

actioncable/lib/rails/generators/channel/templates/assets/channel.coffee

@@ -5,6 +5,9 @@ App.<%= class_name.underscore %> = App.cable.subscriptions.create "<%= class_nam
   disconnected: ->
     # Called when the subscription has been terminated by the server
 
+  received: (data) ->
+    # Called when there's incoming data on the websocket for this channel
+
 <% actions.each do |action| -%>
   <%= action %>: ->
     @perform '<%= action %>'