In Java it is very extended to enforce the use of package-protected instead of private in order to make easier to test methods.
Now i am switching to Groovy and one of the first things i noticed is the public by default access modifier and, later, that package-protected is not very clean and easy to use in Groovy as it was in Java.
Then i also realized about private fields and private methods are not private "bug" --> https://issues.apache.org/jira/browse/GROOVY-1875
... but, of course, this is a bug that may be solved at some moment so i shall not rely on this (Shall i?)
So ... what is the prefered way to test restricted methods in groovy?
Basically the question is if Groovy will in the future ignore private visibility too. You can be sure that in Groovy 2.x this won't be fixed. It might get in a future new major version like Groovy 3. But this version will then contain incompatible fixes anyway, plus it is most likely, that there will be still a way to get the old functionality. So for the near future don't expect that to be "fixed"