### Question:
LimitRowAggregator extends SingleColumnAggregator<LimitRowAggregatorValue> implements Serializable { @Override public void combine(LimitRowAggregatorValue value, LimitRowAggregatorValue other) { value.calculateValue().addAll(other.calculateValue()); } LimitRowAggregator(int limitRow); @Override LimitRowAggregatorValue aggregate(RowTraversal traversal, final Column column); @Override LimitRowAggregatorValue createAggregatorValue(AggregatorValue<?> value); @Override AggregatorType getAggregatorType(); @Override void combine(LimitRowAggregatorValue value, LimitRowAggregatorValue other);  }### Answer:
@Test public void testCombine() { LimitRowAggregatorValue value = new LimitRowAggregatorValue(); LimitRowAggregatorValue other = new LimitRowAggregatorValue(); List<Object> list1 = new ArrayList<>(); List<Object> list2 = new ArrayList<>(); List<Object> list3 = new ArrayList<>(); list1.add("aa"); list2.add("bb"); list2.add("cc"); list3.addAll(list1); list3.addAll(list2); value.setValue(list1); other.setValue(list2); LimitRowAggregator aggregator = new LimitRowAggregator(1); aggregator.combine(value, other); assertEquals(list3, value.calculateValue()); }