@Test
public void shouldSortByLengthFrequency() throws Exception {

    List<List<String>> input = Arrays.asList(Arrays.asList("a", "b", "c"), Arrays.asList("d", "e"), Arrays.asList("f", "g", "h"), Arrays.asList("d", "e"), Arrays.asList("i", "j", "k", "l"), Arrays.asList("m", "n"), Arrays.asList("o"));
    List<List<String>> result = P28.lfsort(input);
    assertThat(result, is(equalTo(Arrays.asList(Arrays.asList("i", "j", "k", "l"), Arrays.asList("o"), Arrays.asList("a", "b", "c"), Arrays.asList("f", "g", "h"), Arrays.asList("d", "e"), Arrays.asList("d", "e"), Arrays.asList("m", "n")))));
}