/** putIfAbsent(null, x) throws NPE */
 public void testPutIfAbsent1_NullPointerException() {
   try {
     ConcurrentNavigableMap c = map5();
     c.putIfAbsent(null, "whatever");
     shouldThrow();
   } catch (NullPointerException success) {
   }
 }
 /** putIfAbsent does not add the pair if the key is already present */
 public void testDescendingPutIfAbsent2() {
   ConcurrentNavigableMap map = dmap5();
   assertEquals("A", map.putIfAbsent(m1, "Z"));
 }
 /** putIfAbsent works when the given key is not present */
 public void testDescendingPutIfAbsent() {
   ConcurrentNavigableMap map = dmap5();
   map.putIfAbsent(six, "Z");
   assertTrue(map.containsKey(six));
 }
 /** putIfAbsent does not add the pair if the key is already present */
 public void testPutIfAbsent2() {
   ConcurrentNavigableMap map = map5();
   assertEquals("A", map.putIfAbsent(one, "Z"));
 }