基于Moq的单元测试中的TargetParameterCountException

Question

We have repositories which have a "Save" method. They also throw a "Created" event whenever an entity is saved.

We have been trying to use Moq to mock out the repository as such....

var IRepository = new Mock<IRepository>();
Request request = new Request();
IRepository.Setup(a => a.Save(request)).Raises(a => a.Created += null, RequestCreatedEventArgs.Empty);

This doesn't seem to work and I always get an exception:

System.Reflection.TargetParameterCountException: Parameter count mismatch.

Any example of mocking events with Moq would be helpful.

Answer 1

A standard event type delegate has two arguments usually: a sender object and a subclass-of-EventArgs object. Moq expects this signature from your event, but only finds one argument and this causes the exception.

Take a look at this code with my comment, it should work:

    public class Request
    {
        //...
    }

    public class RequestCreatedEventArgs : EventArgs
    { 
        Request Request {get; set;} 
    } 

    //=======================================
    //You must have sender as a first argument
    //=======================================
    public delegate void RequestCreatedEventHandler(object sender, RequestCreatedEventArgs e); 

    public interface IRepository
    {
        void Save(Request request);
        event RequestCreatedEventHandler Created;
    }

    [TestMethod]
    public void Test()
    {
        var repository = new Mock<IRepository>(); 
        Request request = new Request();
        repository.Setup(a => a.Save(request)).Raises(a => a.Created += null, new RequestCreatedEventArgs());

        bool eventRaised = false;
        repository.Object.Created += (sender, e) =>
        {
            eventRaised = true;
        };
        repository.Object.Save(request);

        Assert.IsTrue(eventRaised);
    }

Answer 2

It appears that whatever is being returned from RequestCreatedEventArgs.Empty can't be converted to a RequestCreatedEventArgs object. I would expect the following:

class IRepository
{ 
    public event THING Created; 
}
class THING : EventArgs
{ 
    public static THING Empty 
    { 
        get { return new THING(); } 
    } 
}

Verify that THING is the same class in each place in your code as shown above.