Oh well, I didn't know that the kata was broken, but it was a good opportunity to practice. Thank you very much for your time and advice !! I will try to solve what you said, even if the translation isn't going anywhere. By the way, there is no specific reason for the Boolean thing; I just thought it was better to use it in methods than using the primitive. Anyways, thank you very much for your help, and sorry for not responding until today :).

Without specifying whether Ą and Ж are letters, and without the spec of the tested alphabet, I would consider this kata broken (or at least severely underspecified) and I would recommend not translating it until the spec gets fixed :)

If you are still interested in technicl review of tests, there's a couple of points:

• Is there a reason to return a boxed Boolean instead of primitive bool?
• Intentation is off in all snippets except solution setup.
• @Order usually helps in JUnit tests to show fixed tests before random tests.
• Assertion messages of failed tests should provide information about input of the failing test.

Java translation