Estoy tratando de probar el siguiente filtro:

using Microsoft.AspNet.Mvc;
using Microsoft.AspNet.Mvc.Filters;

namespace Hello
{
    public class ValidationFilter : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            if (!filterContext.ModelState.IsValid) {
                filterContext.Result = new BadRequestObjectResult(filterContext.ModelState);
            }
        }
    }
}

Estoy tratando de burlarme del ActionFilterAttribute usando Moq.

Estoy usando Mvc 6.0.0-rc1

Mi primer intento

var context = new ActionExecutingContext(
                    new ActionContext(Mock.Of<HttpContext>(), new RouteData(), new ActionDescriptor()),
                    new IFilterMetadata[] { filter, },
                    new Dictionary<string, object>(),
                    controller: new object());

Pero no pude anular el ModelState. Parece ser de solo lectura:https://github.com/aspnet/Mvc/blob/6.0.0-rc1/src/Microsoft.AspNet.Mvc.Abstraction/ActionContext.cs#L25

Entonces intenté:

var contextMock = new Mock<ActionExecutingContext>(
                    new ActionContext(Mock.Of<HttpContext>(), new RouteData(), new ActionDescriptor()),
                    new IFilterMetadata[] { filter, },
                    new Dictionary<string, object>());

Pero cuando llamofilter.OnActionExecuting(contextMock.Object) Obtuve el siguiente error:

Castle.DynamicProxy.InvalidProxyConstructorArgumentsException : Can not instantiate proxy of class: Microsoft.AspNet.Mvc.Filters.ActionExecutingContext.
      Could not find a constructor that would match given arguments:
      Microsoft.AspNet.Mvc.ActionContext
      Microsoft.AspNet.Mvc.Filters.IFilterMetadata[]
      System.Collections.Generic.Dictionary`2[System.String,System.Object]

¿Cómo probar un filtro que usa ModelState?