I have managed to solve this problem.
The problem was that the navigator was pointing to the wrong node.
It should have been set up like this:
var app = new ApplicationConnection();
var doc = new XPathDocument(_file_path);
var navigator = doc.CreateNavigator();
navigator = navigator.SelectSingleNode("person-info").CreateNavigator();
return PersonInfo.CreateFromXml(app, navigator) as PersonInfo;
So learn from this mistake. Now i can i do some unit testing that involves the PersonInfo object.