In golang the tests are wrong:

Expected
<[]string | len:6, cap:8>: ["a", "b", "b", "c", "c", ""]
to equal
<[]string | len:2, cap:2>: ["ab", "c"]

It does not say anything about ignoring duplicate charachters in the description so the solution should be ["ab", "bc", "c_"] yet it returns fail on that response.