@Test
void mapLong() {

    final ToLong<Long> toLong = l -> l;
    final ToLongMapper<Long, ToLong<Long>, LongUnaryOperator> toLongMapper =
            (ToLongMapper<Long, ToLong<Long>, LongUnaryOperator>)
                    MapperUtil.mapLong(toLong, l -> l);
    assertEquals(MapperType.LONG_TO_LONG, toLongMapper.mapperType());
}