TryValidateModel in unit tests

Hi! :)

I am trying to unit test an action which invokes TryValidateModel but it throws errors all the time and I can't figure out how to make it work (after searching through the code of MVC 6). I am using beta8.

Here are some small examples to illustrate the problem:

Controller:

    public class HomeController : Controller
    {
        [HttpPost]
        public IActionResult Index(SomeModel model)
        {
            this.TryValidateModel(model);

            if (this.ModelState.IsValid)
            {
                return Ok();
            }

            return HttpBadRequest();
        }
    }

Model:

    public class SomeModel
    {
        [Required]
        public int Int { get; set; }

        [Required]
        [StringLength(20, MinimumLength = 5)]
        public string String { get; set; }
    }

Unit test class (with copied code from MVC source tests)

public class ControllersTest
    {
        [Fact]
        public void TryValidateModelTest()
        {
            var controller = GetController(new GenericModelBinder(), new CompositeValueProvider());

            controller.Index(new SomeModel()); // throws exception, test fails

            Assert.False(controller.ModelState.IsValid);
        }

        // code copied from MVC source unit tests but still throws exception
        private static HomeController GetController(IModelBinder binder, IValueProvider provider)
        {
            var metadataProvider = TestModelMetadataProvider.CreateDefaultProvider();
            var httpContext = new DefaultHttpContext();
            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            var viewData = new ViewDataDictionary(metadataProvider, new ModelStateDictionary());
            var tempData = new TempDataDictionary(new HttpContextAccessor(), new SessionStateTempDataProvider());

            var bindingContext = new ActionBindingContext()
            {
                ModelBinder = binder,
                ValueProvider = provider,
                InputFormatters = new List<IInputFormatter>(),
                ValidatorProvider = new DataAnnotationsModelValidatorProvider(
                    options: null,
                    stringLocalizerFactory: null)
            };
            var contr =  new HomeController()
            {
                ActionContext = actionContext,
                BindingContext = bindingContext,
                MetadataProvider = metadataProvider,
                ViewData = viewData,
                TempData = tempData,
                ObjectValidator = new DefaultObjectValidator(new IExcludeTypeValidationFilter[0], metadataProvider)
            };

            return contr;
        }
    }

Full example is available here: LINK

Any suggestions or pointers how to make it work?