### Question:
CollectionOperandNode extends OperandNode { @Override public String toString() { return String.format("(%s)", String.join(",", data)); } CollectionOperandNode(DataType dataType, List<String> data); List<String> getData(); @Override String toString();  }### Answer:
@Test public void testToString() { List<String> data = new ArrayList<>(); data.add("s"); CollectionOperandNode operand = new CollectionOperandNode(DataType.INTEGER, data); assertEquals("(s)", operand.toString()); data.add("t"); operand = new CollectionOperandNode(DataType.INTEGER, data); assertEquals("(s,t)", operand.toString()); }