### Question:
AckRangeSet { @Override public String toString() { return ranges.toString(); } AckRangeSet(); long determineReceiveNextNumber(long receiveNextNumber); void add(long seqNumber, long ackNumber); Collection<AckRange> createSelectiveAckData(); @Override String toString();  }### Answer:
@Test public void testToString() { AckRangeSet set = new AckRangeSet(); set.add(101, 301); ArrayList<AckRange> arr = (ArrayList<AckRange>) set.createSelectiveAckData(); arr.get(0).toString(); set.toString(); }