Unit testing that an event is raised in C#, using reflection
- by Thomas
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?
