@Test
public void lookupTest() throws Exception {

    // loop up before registry
    try {
        abstractRegistry.lookup(null);
        Assertions.fail();
    } catch (Exception e) {
        Assertions.assertTrue(e instanceof NullPointerException);
    }
    List<URL> urlList1 = abstractRegistry.lookup(testUrl);
    Assertions.assertFalse(urlList1.contains(testUrl));
    // loop up after registry
    List<URL> urls = new ArrayList<>();
    urls.add(testUrl);
    abstractRegistry.notify(urls);
    List<URL> urlList2 = abstractRegistry.lookup(testUrl);
    Assertions.assertTrue(urlList2.contains(testUrl));
}