data.addChildUrl(child1);
        data.addChildUrl(child2);
        assertEquals(2, data.getChildUrlSet().size());

        // Remove one child URL
        data.removeChildUrl(child1);
        assertEquals(1, data.getChildUrlSet().size());
        assertFalse(data.getChildUrlSet().contains(child1));
        assertTrue(data.getChildUrlSet().contains(child2));
    }

    public void test_childUrlSetNoDuplicates() {

                }
                final int depth = urlQueue.getDepth() == null ? 1 : urlQueue.getDepth() + 1;
                if (crawlerContext.getMaxDepth() < 0 || depth <= crawlerContext.getMaxDepth()) {
                    // add and filter urls
                    storeChildUrls(crawlerContext, resultData.getChildUrlSet(), urlQueue.getUrl(), depth, resultData.getEncoding());

                                fessConfig.getIndexFieldClickCount(), fessConfig.getIndexFieldFavoriteCount() });
                if (document == null) {
                    storeChildUrlsToQueue(urlQueue, getChildUrlSet(searchEngineClient, id));
                    return true;
                }

                final Date expires = DocumentUtil.getValue(document, fessConfig.getIndexFieldExpires(), Date.class);

        // Execute - should not throw any exception
        processor.process(responseData);

        // Verify child URLs are unchanged
        assertEquals(2, responseData.getChildUrlSet().size());
    }

    public void test_noOpBehavior() {
        // Verify that NullResponseProcessor truly does nothing
        NullResponseProcessor processor = new NullResponseProcessor();

                    logger.info("META(robots=noindex): {}", responseData.getUrl());
                    storeChildUrls(responseData, resultData);
                    throw new ChildUrlsException(resultData.getChildUrlSet(), "#processMetaRobots");
                }
                if (nofollow) {
                    logger.info("META(robots=nofollow): {}", responseData.getUrl());
                    responseData.setNoFollow(true);

                }
                requestDataList = convertChildUrlList(requestDataList);
                resultData.addAllUrl(requestDataList);
            });

            resultData.addAllUrl(responseData.getChildUrlSet());

            final RequestData requestData = responseData.getRequestData();
            resultData.removeUrl(requestData);
            resultData.removeUrl(getDuplicateUrl(requestData));