@Test
  public void testForFunction_Serializable() {
    Navigator<Integer> navigator =
        SerializationUtils.serializedCopy(
            Navigators.forFunction(ImmutableSet.of(1, 2, 3), new MyFun()));

    assertEquals(ImmutableSet.of(1, 2, 3), ImmutableSet.copyOf(navigator.domain()));
    assertEquals(ImmutableSet.of(2, 2), ImmutableSet.copyOf(navigator.related(1)));
    assertEquals(ImmutableSet.of(4, 3), ImmutableSet.copyOf(navigator.related(2)));
    assertEquals(ImmutableSet.of(6, 4), ImmutableSet.copyOf(navigator.related(3)));
  }