@Override
    public void register(URL url) {
        super.register(url);
        registered(url);
    }
@Test
    void testRegister() {
        Set<URL> registered;
        // clear first
        registered = registry.getRegistered();
        for (URL url : registered) {
            registry.unregister(url);
        }

        for (int i = 0; i < 2; i++) {
            registry.register(serviceUrl);
            registered = registry.getRegistered();
            assertTrue(registered.contains(serviceUrl));
        }
        // confirm only 1 register success
        registered = registry.getRegistered();
        assertEquals(1, registered.size());
    }