### Question:
SCMSecurityProtocolServer implements SCMSecurityProtocol { public void stop() { try { LOGGER.info("Stopping the SCMSecurityProtocolServer."); metrics.unregister(); getRpcServer().stop(); } catch (Exception ex) { LOGGER.error("SCMSecurityProtocolServer stop failed.", ex); } } SCMSecurityProtocolServer(OzoneConfiguration conf,
      CertificateServer certificateServer); @Override String getDataNodeCertificate(
      DatanodeDetailsProto dnDetails,
      String certSignReq); @Override String getOMCertificate(OzoneManagerDetailsProto omDetails,
      String certSignReq); @Override String getCertificate(String certSerialId); @Override String getCACertificate(); RPC.Server getRpcServer(); InetSocketAddress getRpcAddress(); void start(); void stop(); void join();  }### Answer:
@Test public void testStop() { securityProtocolServer.stop(); }