Referencing a private class in JUnit

I have a scenario where I want to reference a private class - not test that class.

I am using Spring JDBCTemplate to query db and using a row mapper (which is private class of dao) for mapping the resultset to my object.

Test case is mocking like when(dao.method(query, rowmapper, param)).thenReturn(something)

Possible solutions: Make rowmapper default access and keep test case in the same package.

However my belief is that why to make code changes for the sake of test cases? I was wondering if Java reflection can be of any use in this or not? I couldn't find any thing on that so if someone has already been through such thing then please share.