@SuppressWarnings("EmptyCatchBlock")
 static void ensureNotDirectlyModifiable(NavigableSet<Integer> unmod) {
   try {
     unmod.add(4);
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     unmod.remove(4);
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     unmod.addAll(Collections.singleton(4));
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     unmod.pollFirst();
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     unmod.pollLast();
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     Iterator<Integer> iterator = unmod.iterator();
     iterator.next();
     iterator.remove();
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
   try {
     Iterator<Integer> iterator = unmod.descendingIterator();
     iterator.next();
     iterator.remove();
     fail("UnsupportedOperationException expected");
   } catch (UnsupportedOperationException expected) {
   }
 }
  @SuppressWarnings("EmptyCatchBlock")
  public void testUnmodifiability() {
    TreeSet<Integer> mod = Sets.newTreeSet();
    mod.add(1);
    mod.add(2);
    mod.add(3);

    NavigableSet<Integer> unmod = new UnmodifiableNavigableSet<Integer>(mod);

    mod.add(4);
    assertTrue(unmod.contains(4));
    assertTrue(unmod.descendingSet().contains(4));

    ensureNotDirectlyModifiable(unmod);
    ensureNotDirectlyModifiable(unmod.descendingSet());
    ensureNotDirectlyModifiable(unmod.headSet(2));
    ensureNotDirectlyModifiable(unmod.headSet(2, true));
    ensureNotDirectlyModifiable(unmod.tailSet(2));
    ensureNotDirectlyModifiable(unmod.tailSet(2, true));
    ensureNotDirectlyModifiable(unmod.subSet(1, 3));
    ensureNotDirectlyModifiable(unmod.subSet(1, true, 3, true));

    NavigableSet<Integer> reverse = unmod.descendingSet();
    try {
      reverse.add(4);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      reverse.addAll(Collections.singleton(4));
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      reverse.remove(4);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
  }