@Test
public void testConstantly1() {

    final Supplier<String> supplier = () -> sentinel;
    final Function<Boolean, String> function = Fun.constantly1(supplier);
    final String[] results = Stream.of(Boolean.TRUE, Boolean.FALSE).map(function).toArray(String[]::new);
    assertArrayEquals("results should be [sentinel, sentinel]: " + Arrays.toString(results),
            new String[]{sentinel, sentinel}, results);
}