@Test
public void testUnsubscribeIfUrlNull() throws Exception {

    Assertions.assertThrows(IllegalArgumentException.class, () -> {
        final AtomicReference<Boolean> notified = new AtomicReference<Boolean>(false);
        NotifyListener listener = urls -> notified.set(Boolean.TRUE);
        abstractRegistry.unsubscribe(null, listener);
        Assertions.fail("unsubscribe url == null");
    });
}