}

  public void testTransform_present_functionReturnsNull() {
    assertThrows(NullPointerException.class, () -> Optional.of("a").transform(input -> null));
  }

  public void testTransform_absent_functionReturnsNull() {
    assertEquals(Optional.absent(), Optional.absent().transform(input -> null));
  }

  public void testEqualsAndHashCode() {
    new EqualsTester()