Write to disk in Platform based JUnit tests

I want to create the new file in the user directory, so the one where NB Platform according to documentation writes all its delta from the embedded layer.xml data. (The one where also Windows2Local folder is placed - btw what is needed that this Folder is initialized for test runs?)
At normal runtime this just workes fine but during test runs a virtual nbfs file is created instead of a real file on disk.

I have looked at getting a partial initialized Environment for testing but I could not achieve to reduce the number of started modules to a subset (I only want to use the module under test and its dependencies of course, but not all other modules - but they all get started)