UrlQueueService<UrlQueue<?>> retrieved = CrawlingParameterUtil.getUrlQueueService();
        assertNotNull(retrieved);
        assertSame(service, retrieved);
    }

    public void test_urlQueueService_setNull() {
        // Set a service first
        @SuppressWarnings("unchecked")
        UrlQueueService<UrlQueue<?>> service = new UrlQueueService<UrlQueue<?>>() {
            @Override