public boolean isSubscribed(String groupName, String serviceName) {
        String subId = NamingUtils.getGroupedName(serviceName, groupName);
        return selectorManager.isSubscribed(subId);
    }
@Test
    void testIsSubscribed() {
        List<String> clusters = Collections.singletonList(CLUSTER_STR_CASE);
        EventListener listener = Mockito.mock(EventListener.class);
        NamingSelector selector = NamingSelectorFactory.newClusterSelector(clusters);
        assertFalse(instancesChangeNotifier.isSubscribed(GROUP_CASE, SERVICE_NAME_CASE));
        
        NamingSelectorWrapper wrapper = new NamingSelectorWrapper(SERVICE_NAME_CASE, GROUP_CASE, CLUSTER_STR_CASE,
                selector, listener);
        instancesChangeNotifier.registerListener(GROUP_CASE, SERVICE_NAME_CASE, wrapper);
        assertTrue(instancesChangeNotifier.isSubscribed(GROUP_CASE, SERVICE_NAME_CASE));
    }