private List<Grouping> execute(String groupingExpression) {
        Query query = newQuery();
        GroupingRequest req = GroupingRequest.newInstance(query);
        req.setRootOperation(GroupingOperation.fromString(groupingExpression));
        GroupingCollector collector = new GroupingCollector();
        newExecution(new GroupingExecutor(), collector).search(query);
        return collector.lst;
    }
Tests the internal rewriting of rank properties which happens in the query.prepare() call
(triggered by the exc.search call in the below).
container-search/src/test/java/com/yahoo/search/grouping/vespa/GroupingExecutorTestCase.java