Using a custom ModelMetadataProvider in a unit test

Question

Pretty new to MVC so hopefully this is a simple question.

I have written a custom binding attribute that requires access to the httpContext. In order to inject a mock httpContext during unit tests, I have written an InjectingMetadataProvider that populates the Context property on any of my custom attributes.

I have managed to get this to work in the following test:

[TestMethod]
public void Marker_ShouldBind_Id()
{
    // Arrange
    var formCollection = new NameValueCollection 
    { 
        { "id", "2" }
    };

    var context = new Mock<HttpContextBase>();
    context.Setup(c => c.User).Returns((IPrincipal)null); 

    var metaProvider = new InjectingMetadataProvider(context.Object);
    ModelMetadataProviders.Current = metaProvider;  //why do I need this?

    var bindingContext = new ModelBindingContext
    {
        ModelName     = string.Empty,
        ValueProvider = new NameValueCollectionValueProvider(formCollection, null),
        ModelMetadata = metaProvider.GetMetadataForType(null, typeof(Marker)),
    };

    var binder = new DefaultModelBinder();

    // Act
    var marker = (Marker)binder.BindModel(new ControllerContext(), bindingContext);

    // Assert
    marker.Id.Should().Be(2);
}

However, if I comment out the line that sets my InjectingMetadataProvider to ModelMetadataProviders.Current, then my InjectingMetadataProvider.CreateMetadata() override gets handed a blank list of attributes, and so the test fails because my custom attributes don't get their context set.

Why do I need to set it to Current when I'm using it explicitly anyway? I don't want to be setting static stuff in my tests.

I may be doing something stupid because I'm feeling in the dark a bit at the moment due to my unfamiliarity with the framework.

Did the code below make sense as to why you must specify ModelMetadataProviders.Current? You can see this method in context [here](https://github.com/ASP-NET-MVC/ASP.NET-Mvc-3/blob/master/mvc3/src/SystemWebMvc/Mvc/DefaultModelBinder.cs). — barry, Nov 19 '12 at 15:47

score 1 · Accepted Answer · answered Nov 02 '12 at 15:01

Inside the DefaultModelBinder, a new binding context is created when calling BindComplexElementalModel. Notice that it gets the metadata from the ModelMetadataProviders.Current, and not your custom model metadata provider.

  internal ModelBindingContext CreateComplexElementalModelBindingContext(ControllerContext controllerContext, ModelBindingContext bindingContext, object model) {
        BindAttribute bindAttr = (BindAttribute)GetTypeDescriptor(controllerContext, bindingContext).GetAttributes()[typeof(BindAttribute)];
        Predicate<string> newPropertyFilter = (bindAttr != null)
            ? propertyName => bindAttr.IsPropertyAllowed(propertyName) && bindingContext.PropertyFilter(propertyName)
            : bindingContext.PropertyFilter;

        ModelBindingContext newBindingContext = new ModelBindingContext() {
            ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, bindingContext.ModelType),
            ModelName = bindingContext.ModelName,
            ModelState = bindingContext.ModelState,
            PropertyFilter = newPropertyFilter,
            ValueProvider = bindingContext.ValueProvider
        };

        return newBindingContext;
    }

Using a custom ModelMetadataProvider in a unit test

1 Answers1