@Test
void mapInt() {

    final ToInt<Integer> toInt = i -> i;
    final ToIntMapper<Integer, ToInt<Integer>, IntUnaryOperator> toIntMapper =
            (ToIntMapper<Integer, ToInt<Integer>, IntUnaryOperator>)
                    MapperUtil.mapInt(toInt, s -> s);
    assertEquals(MapperType.INT_TO_INT, toIntMapper.mapperType());
}