How can I setup StaticResourceExtension when unit testing a markup extension that relies on it?

Question

I have written a custom markup extension : CoalesceResourceExtension

[MarkupExtensionReturnType(typeof(object))]
public class CoalesceResourceExtension : MarkupExtension
{
    public CoalesceResourceExtension(string resources)
    {
        this.Resources = resources;
    }

    public string Separator { get; set; }

    [ConstructorArgument("resources")]
    public string Resources { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        if (Resources != null)
        {
            foreach (string resourceName in Resources.Split(new[] { Separator }, StringSplitOptions.RemoveEmptyEntries))
            {
                try
                {
                    if (new StaticResourceExtension(resourceName).ProvideValue(serviceProvider) is object resource)
                    {
                        return resource;
                    }
                }
                catch { }
            }
        }

        return null;
    }
}

But when I come to unit testing CoalesceResourceExtension, I can't seem to find a way to setup the StaticResourceExtension so that it will find the desired mocked resources. Is there a way I can setup things for the StaticResourceExtension to find my mocked resources?

Answer 1

StaticResourceExtension.ProvideValue(IServiceProvider)'s behaviour can be controlled via mocking the IServiceProvider passed by CoalesceResourceExtension to the StaticResourceExtension but you'll also need to mock all the services and objects from the services it uses : IAmbientProvider, IXamlSchemaContextProvider, XamlSchemaContext, ResourceDictionary, XamlType, PropertyInfo and XamlMember. I've built these mocks by watching what path the StaticResourceExtension was taking by both making the mocks strict and watching the exceptions they were throwing when meeting a member that wasn't setup and by looking at StaticResourceExtension's source code.

Here's a method that builds the whole mocked IServiceProvider for every needed key + value pair passed in :

private IServiceProvider MockIServiceProviderForStaticResourceExtension(params KeyValuePair<object, object>[] resources)
{
    Mock<IServiceProvider> serviceProviderMock = new Mock<IServiceProvider>(MockBehavior.Strict);
    Mock<IXamlSchemaContextProvider> xamlSchemaContextProviderMock = new Mock<IXamlSchemaContextProvider>(MockBehavior.Strict);
    Mock<IAmbientProvider> ambientProviderMock = new Mock<IAmbientProvider>(MockBehavior.Strict);
    Mock<XamlSchemaContext> xamlSchemaContextMock = new Mock<XamlSchemaContext>(MockBehavior.Strict);
    xamlSchemaContextMock.Setup(xsc => xsc.GetXamlType(It.IsAny<Type>())).Returns((Func<Type, XamlType>)(t => GetXamlTypeForType(t, xamlSchemaContextMock.Object)));
    ambientProviderMock.Setup(ap => ap.GetAllAmbientValues(null, false, It.IsAny<IEnumerable<XamlType>>(), It.IsAny<XamlMember[]>())).Returns((Func<IEnumerable<XamlType>, bool, IEnumerable<XamlType>, XamlMember[], IEnumerable<AmbientPropertyValue>>)GetAllAmbientValuesImplementation);
    xamlSchemaContextProviderMock.Setup(xscp => xscp.SchemaContext).Returns(xamlSchemaContextMock.Object);
    serviceProviderMock.Setup(s => s.GetService(typeof(IXamlSchemaContextProvider))).Returns(xamlSchemaContextProviderMock.Object);
    serviceProviderMock.Setup(s => s.GetService(typeof(IAmbientProvider))).Returns(ambientProviderMock.Object);
    serviceProviderMock.Setup(s => s.GetService(It.IsNotIn(typeof(IXamlSchemaContextProvider), typeof(IAmbientProvider)))).Returns(null);

    return serviceProviderMock.Object;

    IEnumerable<AmbientPropertyValue> GetAllAmbientValuesImplementation(IEnumerable<XamlType> ceilingTypes, bool searchLiveStackOnly, IEnumerable<XamlType> types, params XamlMember[] properties)
    {
        Mock<ResourceDictionary> resourceDictionaryMock = new Mock<ResourceDictionary>(MockBehavior.Strict);
        resourceDictionaryMock.Protected().Setup("OnGettingValue", false, ItExpr.Is<object>(o => resources.Any(kvp => kvp.Key.Equals(o))), ItExpr.Ref<object>.IsAny, ItExpr.Ref<bool>.IsAny).CallBase();
        foreach (KeyValuePair<object, object> kvp in resources)
        {
            resourceDictionaryMock.Object.Add(kvp.Key, kvp.Value);
        }

        Mock<AmbientPropertyValue> ambientPropertyValueMock = new Mock<AmbientPropertyValue>(MockBehavior.Strict, null, resourceDictionaryMock.Object);
        return new List<AmbientPropertyValue> { ambientPropertyValueMock.Object };
    }

    XamlType GetXamlTypeForType(Type t, XamlSchemaContext xamlSchemaContext)
    {
        Mock<XamlType> xamlTypeMock = new Mock<XamlType>(MockBehavior.Strict, t, xamlSchemaContext);
        xamlTypeMock.Protected().Setup<XamlMember>("LookupMember", true, "Resources", false).Returns((Func<string, bool, XamlMember>)LookupMemberImplementation);
        xamlTypeMock.Protected().Setup<XamlMember>("LookupMember", true, "BasedOn", false).Returns((Func<string, bool, XamlMember>)LookupMemberImplementation);
        xamlTypeMock.Setup(xt => xt.ToString()).CallBase();
        return xamlTypeMock.Object;

        XamlMember LookupMemberImplementation(string name, bool skipReadOnlyCheck)
        {
            Mock<PropertyInfo> propertyInfoMock = new Mock<PropertyInfo>(MockBehavior.Strict);
            propertyInfoMock.Setup(pi => pi.Name).Returns(name);
            propertyInfoMock.Setup(pi => pi.DeclaringType).Returns(t);
            Mock<XamlMember> xamlMemberMock = new Mock<XamlMember>(MockBehavior.Strict, propertyInfoMock.Object, xamlSchemaContext);
            xamlMemberMock.Setup(xm => xm.ToString()).CallBase();
            return xamlMemberMock.Object;
        }
    }
}