TryUpdateModel causing error from unit test cases (Asp.net mvc) - asp.net-mvc-3

Question

I have on post action in controller. Code is as given below
[HttpPost]
public ActionResult Create(Int64 id, FormCollection collection)
{
var data = Helper.CreateEmptyApplicationsModel();
if (TryUpdateModel(data))
{
// TODO: Save data
return RedirectToAction("Edit", "Applications", new { area = "Applications", id = id });
}
else
{
// TODO: update of the model has failed, look at the error and pass back to the view
if (!ModelState.IsValid)
{
if (id != 0) Helper.ShowLeftColumn(data, id);
return View("Create", data);
}
}
return RedirectToAction("Details", "Info", new { area = "Deals", InfoId= id });
}
I wrote test case for this as below
[TestMethod]
public void CreateTest_for_post_data()
{
var collection = GetApplicantDataOnly();
_controller.ValueProvider = collection.ToValueProvider();
var actual = _controller.Create(0, collection);
Assert.IsInstanceOfType(actual, typeof(RedirectToRouteResult));
}
When I debug this single test case, test case passed because condition
if (TryUpdateModel(data)) return true and its goes to if condition.
But when I debug test cases from entire solution this test case failed because it goes to else condition of " if (TryUpdateModel(data))".
I dont know why..
Please help...
Thanks

Answer 1

I've experienced a similar problem which will solve your issue provided you don't need to use a FormCollection.
I haven't used TryUpdateModel ever since the day I learned of the Auto-Binding feature. Auto-binding, in a nutshell pretty much does the work TryUpdateModel would do for you, that is, it'll set a model object according to the values found in the FormCollection as well as attempting to validate the model. And it does this automatically. All you'll have to do is place a parameter in the ActionMethod and it will automatically have it's properties filled with the values found in the FormCollection. Your Action signature will then turn into this:
public ActionResult Create(Int64 id, SomeModel data)
Now you don't need to call TryUpdateModel at all. You still need to check if the ModelState is valid to decide whether or not to redirect or return a view.
[HttpPost]
public ActionResult Create(Int64 id, SomeModel data)
{
if (ModelState.IsValid)
{
// TODO: Save data
return RedirectToAction("Edit", "Applications", new { area = "Applications", id = id });
}
else
{
if (id != 0) Helper.ShowLeftColumn(data, id);
return View("Create", data);
}
}
This won't throw an exception in your unit tests so that's one problem solved. However, there's another problem now. If you run your application using the above code, it'll work just fine. You model will be validated upon entering the Action and the correct ActionResult, either a redirect or a view, will be returned. However, when you try to unit test both paths, you'll find the model will always return the redirect, even when the model is invalid.
The problem is that when unit testing, the model isn't being validated at all. And since the ModelState is by default valid, ModelState.IsValid will always return true in your unit tests and thus will always return a redirect even when the model is invalid.
The solution: call TryValidateModel instead of ModelState.IsValid. This will force your unit test to validate the model. One problem with this approach is that means the model will be validated once in your unit tests and twice in your application. Which means any errors discovered will be recorded twice in your application. Which means if you use the ValidationSummary helper method in your view, your gonna see some duplicated messages listed.
If this is too much to bear, you can clear the ModelState before calling TryValidateModel. There are some problems with doing so because your gonna lose some useful data, such as the attempted value if you clear the ModelState so you could instead just clear the errors recorded in the ModelState. You can do so by digging deep into the ModelState and clearing every error stored in every item like so:
protected void ClearModelStateErrors()
{
foreach (var modelState in ModelState.Values)
modelState.Errors.Clear();
}
I've placed the code in a method so it can be reused by all Actions. I also added the protected keyword to hint that this might be a useful method to place in a BaseController that all your controllers derive from so that they all have access to this method.
Final Solution:
[HttpPost]
public ActionResult Create(Int64 id, SomeModel data)
{
ClearModelStateErrors();
if (ModelState.IsValid)
{
// TODO: Save data
return RedirectToAction("Edit", "Applications", new { area = "Applications", id = id });
}
else
{
if (id != 0) Helper.ShowLeftColumn(data, id);
return View("Create", data);
}
}
NOTE: I realize I didn't shed any light on the root issue. That's because I don't completely understand the root issue. If you notice the failing unit test, it fails because a ArgumentNullException was thrown because the ControllerContext is null and it is passed to a method which throws an exception if the ControllerContext is null. (Curse the MVC team with their damned defensive programming).
If you attempt to mock the ControllerContext, you'll still get an exception, this time a NullReferenceException. Funnily enough, the stack trace for the exception shows that both exceptions occur at the same method, or should I say constructor, located at System.Web.Mvc.ChildActionValueProvider. I don't have a copy of the source code handy so I have no idea what is causing the exception and I've yet to find a better solution than the one I offered above. I personally don't like my solution because I'm changing the way I code my application for the benefit of my unit tests but there doesn't seem to be a better alternative. I bet the real solution will involve mocking some other object but I just don't know what.
Also, before anyone gets any smart ideas, mocking the ValueProvider is not a solution. It'll stop exceptions but your unit tests won't be validating your model and your ModelState will always report that the model is valid even when it isn't.

Answer 2

You might want to clean up your code a bit:
[HttpPost]
public ActionResult Create(int id, FormCollection collection)
{
var data = Helper.CreateEmptyApplicationsModel();
if (!ModelState.IsValid)
{
if (id != 0)
{
Helper.ShowLeftColumn(data, id);
}
return View("Create", data);
}
if (TryUpdateModel(data))
{
return RedirectToAction("Edit", "Applications", new { area = "Applications", id = id });
}
return RedirectToAction("Details", "Info", new { area = "Deals", InfoId= id });
}
Don't use Int64, just use int.
As for your failing test, I would expect your test to fail all the time since TryUpdateModel will return false. As your running the code from a unit test, the controller context for a controller is not available, thus TryUpdateModel will fail.
You need to somehow fake/mock TryUpdateModel so that it does not actually run properly. Instead you "fake" it to return true. Here's some links to help:
How do I Unit Test Actions without Mocking that use UpdateModel?
The above SO answer shows an example using RhinoMocks which is a free mocking framework.
Or this:
http://www.codecapers.com/post/ASPNET-MVC-Unit-Testing-UpdateModel-and-TryUpdateModel.aspx

Answer 3

Debug your tests and check the modelstate errors collection, all the errors that the tryupdatemodel encountered should be there.