@Test
void composeToDouble() {

    final ToDouble<String> toDouble = String::length;
    final ComposeToDouble<String, String, ToDouble<String>> composeToDouble =
            (ComposeToDouble<String, String, ToDouble<String>>)
                    ComposedUtil.composeToDouble(Function.identity(), toDouble);
    assertNotNull(composeToDouble.firstStep());
    assertNotNull(composeToDouble.secondStep());
    assertNull(composeToDouble.apply(null));
    assertNotNull(composeToDouble.apply("test"));
}