Unit Tests

I am brand new to writing unit tests. Can anybody give me an example of a unit test that would check to see that this simple  below method does in fact return an integer ? A bit stupid I know,  I am just trying to get my feet wet here . I am assuming I can use Assert() in some shape or form ?? Any help would be greatly appreciated.
--Jason
public int randomstring() { Random rnd = new Random(); int i = rnd.Next(1, 13); return i; }