public Collection<String> getAllClientsSubscribeService(Service service) {
        return subscriberIndexes.containsKey(service) ? subscriberIndexes.get(service) : new ConcurrentHashSet<>();
    }
@Test
    void testGetAllClientsSubscribeService() {
        
        Collection<String> allClientsSubscribeService = clientServiceIndexesManager.getAllClientsSubscribeService(service);
        
        assertNotNull(allClientsSubscribeService);
        assertEquals(1, allClientsSubscribeService.size());
    }