@Override
    public ClientProtos.GetResponse get(RpcController controller, ClientProtos.GetRequest request)
      throws ServiceException {
      try {
        Thread.sleep(DELAY_GET);
      } catch (InterruptedException e) {
        LOG.error("Sleep interrupted during get operation", e);
      }
      return super.get(controller, request);
    }
This {@link RSRpcServices} class injects delay for Rpc calls and after executes super methods.
hbase-server/src/test/java/org/apache/hadoop/hbase/TestClientOperationTimeout.java