A tool for unit testing in groovy

I am new to Groovy language and I am trying to write tests for java project using it.

The case is: I have really big type lets call it PT which consists of other types. For example

PT
 |__> TypeA a
           |__> String b
           |__> int c
 |_> TypeB d
          |__> double e
          |__> List<Integer> f
 ...

What I want to do is to populate an object of the PT type with some defaults. Let say "str" for strings 1 for ints and so on. The question is if there is a library for groovy that does that based on a provided config ?