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c#unit-testingattributesmockingmoq
Roger Lipscombe
Roger Lipscombe

Reputation: 91925

Can I get Moq to add attributes to the mock class?

I'm writing a command-line interface to my project. The user enters "create project foo", and it finds the controller responsible for "project" and then invokes the Create method, passing "foo" as the first argument.

It relies heavily on attributes and reflection: the controller looks something like this:

[ControllerFor("project")]
class ProjectController
{
    [ControllerAction("create")]
    public object Create(string projectName) { /* ... */ }
}

I'd like to use Moq in the unit tests for the parser, something like this:

Mock<IProjectsController> controller = new Mock<IProjectsController>();
controller.Expect(f => f.Create("foo"));

parser.Register(controller.Object);
parser.Execute("create project foo");

controller.VerifyAll();

Adding the attributes to the interface doesn't appear to work -- they're not inherited by derived classes.

Can I get Moq to add attributes to the class being mocked?

Upvotes: 26

Views: 11283

Answers (1)

Richard Szalay
Richard Szalay

Reputation: 84804

Update: I've just realised that you can actually add attributes to an existing type by using TypeDescriptor.AddAttributes, which can be executed against an instance or a a type:

Mock<IRepository> repositoryMock = new Mock<IRepository>();

CustomAttribute attribute = new CustomAttribute();

// option #1: to the instance
TypeDescriptor.AddAttributes(repositoryMock.Object, attribute );

// option #2: to the generated type
TypeDescriptor.AddAttributes(repositoryMock.Object.GetType(), attributes);

If you need it, AddAttribute returns a TypeDescriptorProvider that can be passed to TypeDescriptor.RemoveProvider to remove the attributes afterwards.

Be aware that Attribute.GetCustomAttributes will not find attributes added at runtime in this way. Instead, use TypeDescriptor.GetAttributes.

Original Answer

I don't belive Moq (or any other mocking framework for that matter) supports custom attributes. I do know that Castle Proxy (the framework commonly used to actually create the class) does support it, but there'd be no way to access it through Moq.

Your best bet is to abstract your method of loading Attributes into an interface (that accepts the Type and the Attribute type) and then mock that.

Edit: For example:

public interface IAttributeStrategy
{
    Attribute[] GetAttributes(Type owner, Type attributeType, bool inherit);
    Attribute[] GetAttributes(Type owner, bool inherit);
}

public class DefaultAttributeStrategy : IAttributeStrategy
{
    public Attribute[] GetAttributes(Type owner, Type attributeType, bool inherit)
    {
        return owner.GetCustomAttributes(attributeType, inherit);
    }

    public Attribute[] GetAttributes(Type owner, bool inherit)
    {
        return owner.GetCustomAttributes(inherit);
    }
}

The class that needs the attributes uses an instance of IAttributeStrategy (either through an IoC container, or having it optionally passed into the constructor). Usually it will be a DefaultAttributeStrategy, but you can now mock IAttributeStrategy in order to override the output.

It might sound convoluted, but adding a layer of abstraction is much easier than attempting to trying to actually mock Attributes.

Upvotes: 33

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