Testing route configuration in ASP.NET WebApi

I am trying to do some unit testing of my WebApi route configuration. I want to test that the route "/api/super" maps to the Get() method of my SuperController. I've setup the below test and am having a few issues.

public void GetTest()
{
    var url = "~/api/super";

    var routeCollection = new HttpRouteCollection();
    routeCollection.MapHttpRoute("DefaultApi", "api/{controller}/");

    var httpConfig = new HttpConfiguration(routeCollection);
    var request = new HttpRequestMessage(HttpMethod.Get, url);

    // exception when url = "/api/super"
    // can get around w/ setting url = "http://localhost/api/super"
    var routeData = httpConfig.Routes.GetRouteData(request);
    request.Properties[HttpPropertyKeys.HttpRouteDataKey] = routeData;

    var controllerSelector = new DefaultHttpControllerSelector(httpConfig);

    var controlleDescriptor = controllerSelector.SelectController(request);

    var controllerContext =
        new HttpControllerContext(httpConfig, routeData, request);
    controllerContext.ControllerDescriptor = controlleDescriptor;

    var selector = new ApiControllerActionSelector();
    var actionDescriptor = selector.SelectAction(controllerContext);

    Assert.AreEqual(typeof(SuperController),
        controlleDescriptor.ControllerType);
    Assert.IsTrue(actionDescriptor.ActionName == "Get");
}

My first issue is that if I don't specify a fully qualified URL httpConfig.Routes.GetRouteData(request); throws a InvalidOperationException exception with a message of "This operation is not supported for a relative URI."

I'm obviously missing something with my stubbed configuration. I would prefer to use a relative URI as it does not seem reasonable to use a fully qualified URI for route testing.

My second issue with my configuration above is I am not testing my routes as configured in my RouteConfig but am instead using:

var routeCollection = new HttpRouteCollection();
routeCollection.MapHttpRoute("DefaultApi", "api/{controller}/");

How do I make use of the assigned RouteTable.Routes as configured in a typical Global.asax:

public class MvcApplication : HttpApplication
{
    protected void Application_Start()
    {
        // other startup stuff

        RouteConfig.RegisterRoutes(RouteTable.Routes);
    }
}

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        // route configuration
    }
}

Further what I have stubbed out above may not be the best test configuration. If there is a more streamlined approach I am all ears.