// Test that the functional interface works correctly
        XContentBuilderCallback callback = (builder, params) -> {
            builder.startObject();
            builder.field("callback", "test");
            builder.endObject();
            return builder;
        };

        assertNotNull(callback);

        // Verify the interface can be used in context

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

   * case of an error.
   *
   * @param event the callback to execute on {@link #dispatch}
   */
  public void enqueue(Event<L> event) {
    enqueueHelper(event, event);
  }

  /**
   * Enqueues an event to be run on currently known listeners, with a label.
   *
   * @param event the callback to execute on {@link #dispatch}

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

     *   <li>Index update operations through callbacks</li>
     *   <li>Error handling and failure logging</li>
     *   <li>Cleanup of old documents after successful crawling</li>
     * </ul>
     */
    protected static class DataCrawlingThread extends Thread {

        /** Configuration for the data store being crawled */
        private final DataConfig dataConfig;

        /** Callback for handling document indexing operations */

        if (queryLambda != null) {
            queryLambda.callback(cq);
        }
        FilterAggregationBuilder builder = regFilterA(name, cq.getQuery());
        if (opLambda != null) {
            opLambda.callback(builder);
        }
        if (aggsLambda != null) {
            SearchLogCA ca = new SearchLogCA();
            aggsLambda.callback(ca);
            ca.getAggregationBuilderList().forEach(builder::subAggregation);

        KeyMatchCQ cq = new KeyMatchCQ();
        queryLambda.callback(cq);
        final Collection<FilterFunctionBuilder> list = new ArrayList<>();
        if (functionsLambda != null) {
            functionsLambda.callback((cqLambda, scoreFunctionBuilder) -> {
                KeyMatchCQ cf = new KeyMatchCQ();
                cqLambda.callback(cf);

        if (queryLambda != null) {
            queryLambda.callback(cq);
        }
        FilterAggregationBuilder builder = regFilterA(name, cq.getQuery());
        if (opLambda != null) {
            opLambda.callback(builder);
        }
        if (aggsLambda != null) {
            ClickLogCA ca = new ClickLogCA();
            aggsLambda.callback(ca);
            ca.getAggregationBuilderList().forEach(builder::subAggregation);

        if (queryLambda != null) {
            queryLambda.callback(cq);
        }
        FilterAggregationBuilder builder = regFilterA(name, cq.getQuery());
        if (opLambda != null) {
            opLambda.callback(builder);
        }
        if (aggsLambda != null) {
            FailureUrlCA ca = new FailureUrlCA();
            aggsLambda.callback(ca);