How do you unit test private methods?

You generally don't unit test private methods directly. Since they are private, consider them an implementation detail. Nobody is ever going to call one of them and expect it to work a particular way.
You should instead test your public interface. If the methods that call your private methods are working as you expect, you then assume by extension that your private methods are working correctly.

http://programmers.stackexchange.com/questions/100959/how-do-you-unit-test-private-methods