}

  public void testGetSubscribers_returnsImmutableSnapshot() {
    StringSubscriber s1 = new StringSubscriber();
    StringSubscriber s2 = new StringSubscriber();
    ObjectSubscriber o1 = new ObjectSubscriber();

    Iterator<Subscriber> empty = registry.getSubscribers("");
    assertFalse(empty.hasNext());

    empty = registry.getSubscribers("");

    registry.register(s1);