How to fake ip address for ApiController?

I am trying to create a web api by System.Web.Http. ​ In a function I use HttpContext.Current.Request.UserHostAddress to get request ip address.

But when I tried to test the controller, I don't know how to fake the ip address to controller.

var controller = new ApplicationMobileStateApiController();
controller.Request = new HttpRequestMessage();
controller.Request.Properties.Add(HttpPropertyKeys.HttpConfigurationKey, new HttpConfiguration());
controller.RequestContext = mockContext;

return controller.Authorization(body);

How can I fake ip address to do this unit test of APIController?