}

    @Override
    public NavigableSet<K> navigableKeySet() {
      return new StandardNavigableKeySet();
    }

    @Override
    public NavigableSet<K> descendingKeySet() {
      return standardDescendingKeySet();
    }

    @Override
    public K firstKey() {
      return standardFirstKey();
    }

    @Override

    assertThat(map.headMap("two", false).values()).containsExactly(3, 5).inOrder();
    assertThat(map.headMap("two", false).descendingMap().values()).containsExactly(5, 3).inOrder();
    assertThat(map.descendingKeySet()).containsExactly("two", "three", "one").inOrder();

    assertEquals(mapEntry("one", 3), map.pollFirstEntry());
    assertEquals(mapEntry("two", 3), map.pollLastEntry());
    assertEquals(1, map.size());
  }

    assertThat(map.headMap("two", false).values()).containsExactly(3, 5).inOrder();
    assertThat(map.headMap("two", false).descendingMap().values()).containsExactly(5, 3).inOrder();
    assertThat(map.descendingKeySet()).containsExactly("two", "three", "one").inOrder();

    assertEquals(mapEntry("one", 3), map.pollFirstEntry());
    assertEquals(mapEntry("two", 3), map.pollLastEntry());
    assertEquals(1, map.size());
  }