@Override
        public Result search(Query query, Execution execution) {
            Result result = execution.search(query);
            result.hits().add(new Hit("sync:0"));
            result.hits().add(new Hit("sync:1"));
            result.hits().add(new Hit("sync:2"));
            return result;
        }
A searcher which returns immediately with future data which can then be filled later,
simulating an async searcher using a separate thread to fill in result data as it becomes available.
container-search/src/test/java/com/yahoo/search/searchchain/test/FutureDataTestCase.java