@Override
      public void start() {
        metrics = Mockito.spy(metrics);
        super.start();
      }
This test is for HBASE-27924, before this JIRA, bytes sent by
{@link NettyHBaseSaslRpcServerHandler} is ignored by {@link MetricsHBaseServer#sentBytes}.
hbase-server/src/test/java/org/apache/hadoop/hbase/ipc/TestSecurityRpcSentBytesMetrics.java