private void addSubscriberIndexes(Service service, String clientId) {
        Set<String> clientIds = subscriberIndexes.computeIfAbsent(service, key -> new ConcurrentHashSet<>());
        // Fix #5404, Only first time add need notify event.
        if (clientIds.add(clientId)) {
            NotifyCenter.publishEvent(new ServiceEvent.ServiceSubscribedEvent(service, clientId));
        }
    }
@Test
    void testAddSubscriberIndexes() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        String clientId = "clientId";
        Class<ClientServiceIndexesManager> clientServiceIndexesManagerClass = ClientServiceIndexesManager.class;
        Method addSubscriberIndexes = clientServiceIndexesManagerClass.getDeclaredMethod("addSubscriberIndexes", Service.class,
                String.class);
        addSubscriberIndexes.setAccessible(true);
        addSubscriberIndexes.invoke(clientServiceIndexesManager, service, clientId);
        
        Collection<String> allClientsSubscribeService = clientServiceIndexesManager.getAllClientsSubscribeService(service);
        
        assertNotNull(allClientsSubscribeService);
        assertEquals(2, allClientsSubscribeService.size());
    }