### Question:
Aggregate extends Operator { public TupleDesc getTupleDesc() { if (td != null) { return td; } Type[] types; String[] names; String aggName = child_td.getFieldName(agIndex); if (gbIndex == Aggregator.NO_GROUPING) { types = new Type[]{Type.INT_TYPE}; names = new String[]{aggName}; } else { types = new Type[]{gbFieldType, Type.INT_TYPE}; names = new String[]{child_td.getFieldName(gbIndex), aggName}; } td = new TupleDesc(types, names); return td; } Aggregate(DbIterator child, int agIndex, int gbIndex, Aggregator.Op aggreOp); int groupFieldIndex(); String groupFieldName(); int aggregateFieldIndex(); String aggregateFieldName(); Aggregator.Op aggregateOp(); static String nameOfAggregatorOp(Aggregator.Op aggreOp); void open(); void rewind(); TupleDesc getTupleDesc(); void close(); @Override DbIterator[] getChildren(); @Override void setChildren(DbIterator[] children);  }### Answer:
@Test public void getTupleDesc() { Aggregate op = new Aggregate(scan1, 0, 0, Aggregator.Op.MIN); TupleDesc expected = Utility.getTupleDesc(2); TupleDesc actual = op.getTupleDesc(); assertEquals(expected, actual); }