createroutes.cs

var _dependencyResolver = DependencyResolver.Current; //Get this from private variable that you can override when unit testing

routes.MapRoute(
  "Countries",
  "countries/{country}",
  new {
      controller = "Countries",
      action = "Index"
  },
  new {
      country = new InjectedRouteConstraint<CountryRouteConstraint>(_dependencyResolver);
  }
);