Verify an event was raised by mocked object

Question

In my unit test how can I verify that an event is raised by the mocked object.

I have a View(UI) --> ViewModel --> DataProvider --> ServiceProxy. ServiceProxy makes async call to serivce operation. When async operation is complete a method on DataProvider is called (callback method is passed as a method parameter). The callback method then raise and event which ViewModel is listening to.

For ViewModel test I mock DataProvider and verify that handler exists for event raised by DataProvider. When testing DataProvider I mock ServiceProxy, but how can I test that callback method is called and event is raised.

I am using RhinoMock 3.5 and AAA syntax

Thanks

-- DataProvider --

public partial class DataProvider
{
    public event EventHandler<EntityEventArgs<ProductDefinition>> GetProductDefinitionCompleted;

    public void GetProductDefinition()
    {
        var service = IoC.Resolve<IServiceProxy>();
        service.GetProductDefinitionAsync(GetProductDefinitionAsyncCallback);
    }

    private void GetProductDefinitionAsyncCallback(ProductDefinition productDefinition, ServiceError error)
    {
        OnGetProductDefinitionCompleted(this, new EntityEventArgs<ProductDefinition>(productDefinition, error));
    }

    protected void OnGetProductDefinitionCompleted(object sender, EntityEventArgs<ProductDefinition> e)
    {
        if (GetProductDefinitionCompleted != null)
            GetProductDefinitionCompleted(sender, e);
    }
}

-- ServiceProxy --

public class ServiceProxy : ClientBase<IService>, IServiceProxy
{
    public void GetProductDefinitionAsync(Action<ProductDefinition, ServiceError> callback)
    {
        Channel.BeginGetProductDefinition(EndGetProductDefinition, callback);
    }

    private void EndGetProductDefinition(IAsyncResult result)
    {
        Action<ProductDefinition, ServiceError> callback =
            result.AsyncState as Action<ProductDefinition, ServiceError>;

        ServiceError error;
        ProductDefinition results = Channel.EndGetProductDefinition(out error, result);

        if (callback != null)
            callback(results, error);
    }
}

Answer 1

The following example sets up an IService stub which will simply invoke any callback that is passed to it when IService.AsyncOperationWithCallBack(Action callback) is called.

// arrange
var serviceStub = MockRepository.GenerateStub<IService>();
serviceStub.Stub(x => x.AsyncOperationWithCallBack(Arg<Action>.Is.NotNull))
    .WhenCalled(
        invokation =>
        {
            var callback = (Action)invokation.Arguments[0];
            callback();
        });

var dataProvider = new DataProvider(serviceStub);  

// act
bool raised = false;
dataProvider.MyEvent += delegate { raised = true; };
dataProvider.DoSomething();

// assert
serviceStub.AssertWasCalled(
    x=>x.AsyncOperationWithCallBack(Arg<Action>.Is.NotNull));
Assert.IsTrue(raised);

Answer 2

It sounds like you have two different unit tests to write:

1. Service Proxy unit test: This test will make sure that the callback sent in to the ServiceProxy will be called upon completion of the async call.

2. Data Provider unit test: This test will make sure that when a certain method is called, an event is raised (assuming there were some subscribers).

Which one are you looking for help on?

EDIT:

For item #1, I don't see that you'd need any mocking. Simply provide a callback that sets some variable to true when called:

// arrange
IServiceProxy serviceProxy = new ServiceProxy();
bool callbackMade;

// act
serviceProxy.GetDataAsync(() => callbackMade = true);

// assert
Assert.IsTrue(callbackMade);

For item #2, again, just subscribe to the event in your unit test and make sure the event is called:

// arrange
DataProvider dp = new DataProvider();
bool eventRaised;
dp.DataReturned += (s,e) => eventRaised = true;

// act
dp.DoSomethingThatShouldRaiseEvent();

// assert
Assert.IsTrue(eventRaised)

I don't know the signatures of your events/callbacks so I just made some guesses.