@Test
void toSortedMapByKey() {

    final Comparator<String> keyComparator = Comparator.reverseOrder();
    final Map<String, Integer> expected = refStream().map(Map.Entry::getKey).sorted(keyComparator).map(k -> entry(k, stringToInt.get(k))).collect(TO_MAP);
    final Map<String, Integer> actual = instance.toSortedMapByKey(keyComparator);
    assertEquals(expected, actual);
    assertTrue(actual instanceof NavigableMap);
}