@Test
public void testConstantly2() {

    final Supplier<String> supplier = () -> sentinel;
    final BiFunction<Boolean, Boolean, String> function = Fun.constantly2(supplier);
    final String[] results = Stream.of(
            Fun.toEntry(Boolean.TRUE, Boolean.FALSE),
            Fun.toEntry(Boolean.FALSE, Boolean.TRUE)
    ).map(mapEntry(function)).toArray(String[]::new);
    assertArrayEquals("results should be [sentinel, sentinel]: " + Arrays.toString(results),
            new String[]{sentinel, sentinel}, results);
}