@Test
    public void dedup_whenInputContainsDuplicatedChars() {
        String word = "aaa";
        assertEquals("[[a, a]]", combination.combine(word, 2).toString());
        assertEquals("[[a, a, a], [a, a, b], [a, b, b], [b, b, b]]", combination.combine("ababbbba", 3).toString());
    }