.that(spliterator.characteristics() & expectedCharacteristics)
        .isEqualTo(expectedCharacteristics);
  }

  @GwtIncompatible
  @J2ktIncompatible
  public void testKeySetCharacteristics() {
    int expectedCharacteristics = Spliterator.ORDERED | Spliterator.NONNULL;
    assertThat(
            immutableEnumMap(ImmutableMap.of(AnEnum.A, "a"))
                    .keySet()