@Override
    public List<ServiceDTO> getServiceInstances(String serviceId) {
        try {
            List<Instance> instances = namingService.selectInstances(serviceId,true);
            List<ServiceDTO> serviceDTOList = Lists.newLinkedList();
            instances.forEach(instance -> {
                ServiceDTO serviceDTO = this.toServiceDTO(instance, serviceId);
                serviceDTOList.add(serviceDTO);
            });
            return serviceDTOList;
        } catch (NacosException ex) {
            logger.error(ex.getMessage(),ex);
        }
        return Collections.emptyList();
    }
@Test
    public void testGetServiceInstancesWithInvalidServiceId() {
        assertTrue(nacosDiscoveryService.getServiceInstances(someServiceId).isEmpty());
    }