Can't you print the input? Your code probably is failing because of this:

However you could also receive inputs that are not strings.

I'm passing the sample test, but fail at the unhappy and random test.
The issue is that I don't know what are thos tests and where am failing at.

no issue here.

Some general notes (generic message):

Seems you're "rather new" to cw, so here are some general guidelines about the comments:

• Issue: problem in the kata itself (description, wrong tests, wrong internal solution...)
• Suggestions: well, I guess that part is clear
• Question anything else that is related to you having a problem solving a kata -> that's you, currently.

When you post issues:

• provide ALL the useful information:
  • language
  • input
  • outputs (actual expected) when relevant
  • error message when relevant
• check, DOUBLE check that this IS an issue, meaning that the problem is in the kata itself and not in your code. If it's in your code, post rather a question
• if you pass this step, you still have to prove/explain what the issue is (and if you can provide fixes, it's even better)

When you post a question: well, most of the above apply too x)

When you post code, use proper github markdown, so that it's readable.

to see the inputs: System.out.println(...) / eidt: woops, you're using C#, not java => Console.Write(...)

cheers