public void testSingletonMapFirst() {
    assertEquals(a, navigableMap.firstEntry());
  }

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

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {