Unit testing that an event is raised in C#, using reflection

Posted by Thomas on Stack Overflow See other posts from Stack Overflow or by Thomas
Published on 2010-04-02T14:11:16Z Indexed on 2010/04/02 14:13 UTC
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I want to test that setting a certain property (or more generally, executing some code) raises a certain event on my object. In that respect my problem is similar to http://stackoverflow.com/questions/248989/unit-testing-that-an-event-is-raised-in-c, but I need a lot of these tests and I hate boilerplate. So I'm looking for a more general solution, using reflection.

Ideally, I would like to do something like this:

[TestMethod]
public void TestWidth() {
    MyClass myObject = new MyClass();
    AssertRaisesEvent(() => { myObject.Width = 42; }, myObject, "WidthChanged");
}

For the implementation of the AssertRaisesEvent, I've come this far:

private void AssertRaisesEvent(Action action, object obj, string eventName)
{
    EventInfo eventInfo = obj.GetType().GetEvent(eventName);
    int raisedCount = 0;
    Action incrementer = () => { ++raisedCount; };
    Delegate handler = /* what goes here? */;

    eventInfo.AddEventHandler(obj, handler);
    action.Invoke();
    eventInfo.RemoveEventHandler(obj, handler);

    Assert.AreEqual(1, raisedCount);
}

As you can see, my problem lies in creating a Delegate of the appropriate type for this event. The delegate should do nothing except invoke incrementer.

Because of all the syntactic syrup in C#, my notion of how delegates and events really work is a bit hazy. How to do this?

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