@Test
void iterator() {

    final List<Map.Entry<String, Integer>> expected = refStream().collect(Collectors.toList());
    final List<Map.Entry<String, Integer>> actual = new ArrayList<>();
    final Iterator<Map.Entry<String, Integer>> iterator = instance.iterator();
    while (iterator.hasNext()) {
        actual.add(iterator.next());
    }
    assertEquals(expected, actual);
}