The brackets highlight the difference between both results, that's from JUnit, and they're not part of neither of those values. Your code is failing the first assertion in testOddString tests, not a kata issue. This test:

       String s = "abcde";
       assertEquals("Should handle odd string","[ab, cd, e_]", Arrays.toString(StringSplit.solution(s)));

You can see there that for "abcde"should be ["ab", "cd", "e_"] exactly like the last example in the description.