After using Automapper to map a ViewModel how and what should I test?


After using Automapper to map a ViewModel how and what should I test?



I am attempting to test the Index action of a controller. The action uses AutoMapper to map a domain Customer object to a view model TestCustomerForm. While this works I am concerned about the best way to test the results that I am receiving from the Index action.

The controller's index action looks like this:

public ActionResult Index() {     TestCustomerForm cust = Mapper.Map<Customer,         TestCustomerForm>(_repository.GetCustomerByLogin(CurrentUserLoginName));      return View(cust); } 

And its TestMethod looks like this:

[TestMethod] public void IndexShouldReturnCustomerWithMachines() {     // arrange     var customer = SetupCustomerForRepository(); // gets a boiler plate customer     var testController = CreateTestController();      // act     ViewResult result = testController.Index() as ViewResult;      // assert     Assert.AreEqual(customer.MachineList.Count(),         (result.ViewData.Model as TestCustomerForm).MachineList.Count()); } 

In the CreateTestController method I use Rhino.Mocks to mock a customer repository and set it up to return the customer from SetupCustomerForRepository. In this manner I know that the repository will return the intended customer when the Index action calls _repository.GetCustomerByLogin(CurrentUserLoginName). Therefore, I figure asserting an equal count is adequate to satisfy IndexShouldReturnCustomerWithMachines.

All of that said I am concerned as to what I should be testing.

  1. It seems presumptuous to cast the result.ViewData.Model as TestCustomerForm. Is this really an issue? This concerns me because in this instance I am not truly doing test driven development and it seems like I am counting on a particular implementation to satisfy the test.
  2. Are there more appropriate tests to ensure correct mapping?
  3. Should I be testing each mapped property from the TestCustomerForm?
  4. Are there more general controller action tests that I should be doing?



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1:



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This is one of the reasons why we move AutoMapper into a custom ActionResult or an ActionFilter.


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At some point, you only really want to test that you mapped Foo to FooDto, but not necessarily test the actual mapping.


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By moving AutoMapper into the layer boundaries (such as between controller an view), you can merely test what you're telling AutoMapper to do..
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This is similar to testing a ViewResult.


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You don't test from a controller that a view was rendered, but rather that you told MVC to render such-and-such view.


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Our action result becomes:.
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public class AutoMapViewResult : ActionResult {     public Type SourceType { get; private set; }     public Type DestinationType { get; private set; }     public ViewResult View { get; private set; }      public AutoMapViewResult(Type sourceType, Type destinationType, ViewResult view)     {         SourceType = sourceType;         DestinationType = destinationType;         View = view;     }      public override void ExecuteResult(ControllerContext context)     {         var model = Mapper.Map(View.ViewData.Model, SourceType, DestinationType);          View.ViewData.Model = model;          View.ExecuteResult(context);     } } 
With a helper method on a base controller class:.
protected AutoMapViewResult AutoMapView<TDestination>(ViewResult viewResult) {     return new AutoMapViewResult(viewResult.ViewData.Model.GetType(), typeof(TDestination), viewResult); } 
Which then makes the controller now only specify what to map to/from, instead of performing the actual mapping:.
public ActionResult Index(int minSessions = 0) {     var list = from conf in _repository.Query()                 where conf.SessionCount >= minSessions                 select conf;      return AutoMapView<EventListModel[]>(View(list)); } 
At this point, I only need to test, "make sure that you're mapping this Foo object to this destination FooDto type", without needing to actually perform the mapping.. EDIT:. Here's an example of a test snippet:.
var actionResult = controller.Index();  actionResult.ShouldBeInstanceOf<AutoMapViewResult>();  var autoMapViewResult = (AutoMapViewResult) actionResult;  autoMapViewResult.DestinationType.ShouldEqual(typeof(EventListModel[])); autoMapViewResult.View.ViewData.Model.ShouldEqual(queryResult); autoMapViewResult.View.ViewName.ShouldEqual(string.Empty); 


2:


I would probably separate the coupling between AutoMapper and the controller by introducing an abstraction:.
public interface IMapper<TSource, TDest> {     TDest Map(TSource source); }  public CustomerToTestCustomerFormMapper: IMapper<Customer, TestCustomerForm> {     static CustomerToTestCustomerFormMapper()     {         // TODO: Configure the mapping rules here     }      public TestCustomerForm Map(Customer source)     {         return Mapper.Map<Customer, TestCustomerForm>(source);     } } 
Next you pass this into the controller:.
public HomeController: Controller {     private readonly IMapper<Customer, TestCustomerForm> _customerMapper;     public HomeController(IMapper<Customer, TestCustomerForm> customerMapper)     {         _customerMapper = customerMapper;     }      public ActionResult Index()     {         TestCustomerForm cust = _customerMapper.Map(             _repository.GetCustomerByLogin(CurrentUserLoginName)         );         return View(cust);     } } 
And in your unit test you would use your favorite mocking framework to stub this mapper..



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