This also happens if you use []rune to store the output.
Need to use []byte, then it'd pass.

Hello, I'd like to request for this issue to be unflagged, it's not a spoiler, it's a problem with the tests. It's nearly impossible to solve it without knowing that.

This problem actually blocks correct solutions, I'll try to explain why below:

If you convert every single byte and append it to a string (like we do in other languages) and then return that string, it fails.
If you append them to a byte array and then convert the whole thing to a string, it passes.

If I had to guess, that's probably because when it handles individual extended ASCII chars, it converts them to the "\uFFFF" format, but for some reason when they're part of a slice/array conversion it leaves them as "\xFF"

Does not work with "step-daughter" test case.

Apologies for the late reply; please contact @kazk with regards to issues related to the Go translation of this Kata as I have no knowledge of this programming language.

In Go implementation we are asked to return string, but actually tests check for byte array, so if you work with strings in your solution, you'll get working program which can't pass through the tests.
To complete this Kata we need to create byte array, then convert it to string, pass it to tests, which convert our string to byte array. This is a little bit dumb.