### Question:
GroupedTopNBuilder { public Iterator<Page> buildResult() { return new ResultIterator(); } GroupedTopNBuilder(
            List<Type> sourceTypes,
            PageWithPositionComparator comparator,
            int topN,
            boolean produceRowNumber,
            GroupByHash groupByHash); Work<?> processPage(Page page); Iterator<Page> buildResult(); long getEstimatedSizeInBytes();  }### Answer:
@Test public void testEmptyInput() { GroupedTopNBuilder groupedTopNBuilder = new GroupedTopNBuilder( ImmutableList.of(BIGINT), (left, leftPosition, right, rightPosition) -> { throw new UnsupportedOperationException(); }, 5, false, new NoChannelGroupByHash()); assertFalse(groupedTopNBuilder.buildResult().hasNext()); }