public void testPollFirstUnsupported() {
    assertThrows(UnsupportedOperationException.class, () -> navigableSet.pollFirst());
  }

  @CollectionSize.Require(SEVERAL)
  public void testLowerHole() {
    resetWithHole();
    assertEquals(null, navigableSet.lower(a));
    assertEquals(a, navigableSet.lower(b));
    assertEquals(a, navigableSet.lower(c));
  }

  @CollectionSize.Require(SEVERAL)

  public void testPollFirstUnsupported() {
    assertThrows(UnsupportedOperationException.class, () -> navigableSet.pollFirst());
  }

  @CollectionSize.Require(SEVERAL)
  public void testLowerHole() {
    resetWithHole();
    assertEquals(null, navigableSet.lower(a));
    assertEquals(a, navigableSet.lower(b));
    assertEquals(a, navigableSet.lower(c));
  }

  @CollectionSize.Require(SEVERAL)