Question

When testing a class that uses a Moq dependency, I’d like the class to supply the arguments to a Moq method, rather than creating the arguments myself in the test case.

I have an interface, that has one method, which takes one argument.

public interface IMessageForwardProxy
{
    IMessage Send(IMessage request);
}

I have a class that calls this method with a number of different arguments depending on the method called on the class. For instance:

public class Messenger 
{
    private IMessageForwardProxy _link;

    public Messenger(IMessageForwardProxy proxy) { _link = proxy; }

    public bool DeliverSomeMessage() {
        IMessage m1 = new MessageOne();
        var response = _link.Send(m1);
        return response.Succeeded;
    }

    public bool DeliverSomeOtherMessage() {
        IMessage m2 = new MessageTwo();
        var response = _link.Send(m2);
        return response.Succeeded;
    }
}

Now as you can see, the Messenger class is responsible for creating the arguments that are passed to the Send method of the interface. When I’m testing this Messenger class, I would like to Mock the IMessageForwardProxy’s Send method, without providing the argument in my tests. I see providing the argument as coupling my tests to the implementation (and duplicating work).

If I want to test the DeliverSomeOtherMessage method on the Messenger class, how would I mock the IMessageForwardProxy?

[Test]
public void TestDeliverSomeOtherMessage() {
    var mockProxy = new Mock<IMessageForwardProxy>();

    // This is what I want to avoid, since the method I'm testing creates this argument
    IMessage m2 = new MessageTwo(); 
    mockProxy.Setup(m => m.Send(m2)).Returns(new ReturnMessageTwo());

    // Can I do something like this instead? Define the signature, but not the param?
    mockProxy.Setup(m => m.Send(typeof(IMessage))).Returns(new ReturnMessageTwo());

    var messenger = new Messenger(mockProxy.Object);
    Assert.True(messenger.DeliverSomeOtherMessage());

}

Answer 1

You can use It.IsAny<IMessage>()

Like this:

mockProxy.Setup(m => m.Send(It.IsAny<IMessage>())).Returns(new ReturnMessageTwo());