done (new String("needle") is enough to create a distinct object)

The one-liner requirement is stupid.

There are no random tests.

It should append the nonce to the content

How is the nonce appended to the content? a int can't be appended to the string directly.

These are both issues.

It could be more clear what the possible versions of rose there are, in the test case there is only rose

That's true, i did that xD

Nice kata and nice introduction for beginners to crypto-related APIs. One thing to improve tho: description on ComputeHash says: "It should append the nonce to the content". I think it would be nice to specify what does "append nocne to the content" mean, because there are many possible "concatenation" operations for the (string, uint) pair. Is it content.append(noce.toString(some format))? Or maybe content.bytes.concat(nonce as bytes)? Or maybe even something else?

And yeah, no random tests ;)

without seeing your soluiton, it's impossible to answer (don't forget the spoiler flag)

This kata is very simple, but when I run my solution in IDE with test data my solution work is right, but when I copy-paste my solution to "codewars" on second case (when I get "rOsE") my solution return "false" O.o. I thought that "O" is zero, but it's letter.

The issue with that, it also tells people that " " should equal "". Which, from a programmer's perspective, is nonsense.