Fixed bank-account tests

Update the Tests according to the How-to. If i miss something then please let me know.

What do you mean? What do you see is misleading or confusing? Without seeing what you are doing, it is very hard for us to know if you have missed something.

I hope you give some hints!

@kotp Kevin answered our call to update the test cases for some of the exercises and already submittted a PR.

Thanks @KevDi, vaeng or I will review that.

Yeah sorry forgot to mention the Issue to which this changes belong.