}

  public void testDescendingMap() {
    NavigableMap<String, Integer> map = create();
    NavigableMap<String, Integer> descendingMap = map.descendingMap();
    assertTrue(descendingMap instanceof SynchronizedNavigableMap);
    assertSame(mutex, ((SynchronizedNavigableMap<String, Integer>) descendingMap).mutex);
  }

  public void testFirstEntry() {
    create().firstEntry();
  }

  public void testFirstKey() {

        assertThat(navigableMap.headMap(key, inclusive).descendingMap().entrySet())
            .containsExactlyElementsIn(expected.headMap(key, inclusive).descendingMap().entrySet())
            .inOrder();
        assertThat(navigableMap.tailMap(key, inclusive).descendingMap().entrySet())
            .containsExactlyElementsIn(expected.tailMap(key, inclusive).descendingMap().entrySet())
            .inOrder();
      }
    }
  }

    return new AsMapOfRanges(entriesByLowerBound.values());
  }

  @Override
  public Map<Range<K>, V> asDescendingMapOfRanges() {
    return new AsMapOfRanges(entriesByLowerBound.descendingMap().values());
  }

  private final class AsMapOfRanges extends IteratorBasedAbstractMap<Range<K>, V> {

    final Iterable<Entry<Range<K>, V>> entryIterable;

    return new AsMapOfRanges(entriesByLowerBound.values());
  }

  @Override
  public Map<Range<K>, V> asDescendingMapOfRanges() {
    return new AsMapOfRanges(entriesByLowerBound.descendingMap().values());
  }

  private final class AsMapOfRanges extends IteratorBasedAbstractMap<Range<K>, V> {

    final Iterable<Entry<Range<K>, V>> entryIterable;