@Test
void mapIntToDouble() {

    final ToInt<Integer> toInt = i -> i;
    final ToDoubleMapper<Integer, ToInt<Integer>, IntToDoubleFunction> toDoubleMapper =
            (ToDoubleMapper<Integer, ToInt<Integer>, IntToDoubleFunction>)
                    MapperUtil.mapIntToDouble(toInt, i -> 1);
    assertEquals(MapperType.INT_TO_DOUBLE, toDoubleMapper.mapperType());
}