public void testSingletonMapLast() {
    assertEquals(a, navigableMap.lastEntry());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonMapPollLast() {
    assertEquals(a, navigableMap.pollLastEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(SEVERAL)
  public void testFirst() {