@Override
        public Result search(Query query, Execution execution) {
            ++queryCount;
            if (query.getHits() == 0) {
                return new Result(query);
            } else {
                return new Result(query, ErrorMessage.createIllegalQuery("Did not request zero hits."));
            }
        }
Simulates the return when grouping is used for aggregation purposes and there is a plain hit list in addition:
The returned result contains both regular hits at the top level (from non-grouping)
and groups contained aggregation information.
container-search/src/test/java/com/yahoo/prelude/searcher/test/FieldCollapsingSearcherTestCase.java