public void testSingletonMapPollFirst() {
    assertEquals(a, navigableMap.pollFirstEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {
    assertNull(navigableMap.lowerEntry(k0()));
    assertNull(navigableMap.lowerKey(k0()));
    assertEquals(a, navigableMap.floorEntry(k0()));
    assertEquals(a.getKey(), navigableMap.floorKey(k0()));