@Override
    public void unregister(URL url) {
        super.unregister(url);
        unregistered(url);
    }
@Test
    void testUnregister() {
        Set<URL> registered;

        // register first
        registry.register(serviceUrl);
        registered = registry.getRegistered();
        assertTrue(registered.contains(serviceUrl));

        // then unregister
        registered = registry.getRegistered();
        registry.unregister(serviceUrl);
        assertFalse(registered.contains(serviceUrl));
    }