Question

I am working through Steve Sanderson’s book Pro ASP.NET MVC Framework and I having some issues with two unit tests which produce errors.

In the example below it tests the CheckOut ViewResult:

[AcceptVerbs(HttpVerbs.Post)]
public ViewResult CheckOut(Cart cart, FormCollection form)
{
        // Empty carts can't be checked out
        if (cart.Lines.Count == 0)
        {
            ModelState.AddModelError("Cart", "Sorry, your cart is empty!");
            return View();
        }

        // Invoke model binding manually
        if (TryUpdateModel(cart.ShippingDetails, form.ToValueProvider()))
        {
            orderSubmitter.SubmitOrder(cart);
            cart.Clear();
            return View("Completed");
        }
        else // Something was invalid
            return View();
}

with the following unit test

[Test]
public void Submitting_Empty_Shipping_Details_Displays_Default_View_With_Error()
{
    // Arrange
    CartController controller = new CartController(null, null);
    Cart cart = new Cart();
    cart.AddItem(new Product(), 1);
    // Act
    var result = controller.CheckOut(cart, new FormCollection {
        { "Name", "" }                                               
    });
    // Assert
    Assert.IsEmpty(result.ViewName);
    Assert.IsFalse(result.ViewData.ModelState.IsValid);
}

I have resolved any issues surrounding TryUpdateModel by upgrading to ASP.NET MVC 2 (Release Candidate 2) and the website runs as expected.

The associated error messages are:

Tests.CartControllerTests.Submitting_Empty_Shipping_Details_Displays_Default_View_With_Error: 
System.ArgumentNullException : Value cannot be null.
Parameter name: controllerContext

and the more detailed

at System.Web.Mvc.ModelValidator..ctor(ModelMetadata metadata, ControllerContext controllerContext)
at System.Web.Mvc.DefaultModelBinder.OnModelUpdated(ControllerContext controllerContext, ModelBindingContext bindingContext)
at System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
at System.Web.Mvc.Controller.TryUpdateModel[TModel](TModel model, String prefix, String[] includeProperties, String[] excludeProperties, IValueProvider valueProvider)
at System.Web.Mvc.Controller.TryUpdateModel[TModel](TModel model, IValueProvider valueProvider)
at WebUI.Controllers.CartController.CheckOut(Cart cart, FormCollection form)

Has anyone run into a similar issue or gotten the test to pass?

Answer 1

You have to mock the HttpContext of the Controller to write such tests. The MvcContrib library makes it quite easy.

Another option that I prefer is to extract the logic done by “TryUpdateModel” into a custom ModelBinder. You can then test the logic of your checkout action method separately from the logic that update your model.
No HttpContext needed.