@Override
 public void serveSubscribeRequest(
     ByteString topic,
     SubscribeRequest subRequest,
     MessageSeqId consumeSeqId,
     Callback<SubscriptionData> callback,
     Object ctx) {
   if (fail) {
     callback.operationFailed(ctx, new PubSubException.ServiceDownException("Asked to fail"));
     return;
   }
   super.serveSubscribeRequest(topic, subRequest, consumeSeqId, callback, ctx);
 }