@Test
    public void dedup_whenInputContainsDuplicatedChars() {
        List<Character> chars = new ArrayList<Character>(Arrays.asList('a', 'b', 'b'));
        String expected = "[[a, b, b], [b, a, b], [b, b, a]]";
        String actual = permutation.permute(chars).toString();
        assertEquals(expected, actual);
    }