Add more Java port tests

[vityaman]

Java port was translated into the Dart with the MR

• Provide support for Dart language #164

Actual Java port has an only unit test which is not quite reliable. So it would be nice to have more tests in Java port because it implies more tests for the Dart port. Also as Java is so popular language, there could be other languages ports in future translated from Java (I know at least one).

[mike-lischke]

I agree and I'm ready for PRs.