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copied!<p>You didn't post your tests, so I'm unclear what you are trying to test, but most-likely you are trying to test one of the following things:</p> <ol> <li>That the code you are testing subscribes at all</li> <li>That the code you are testing reacts to events appropriately</li> </ol> <p>In either case, you are going to want to <em>mock the EventAggregator</em>. Because the Event isn't what you want to test, but rather the code that utilizes it, you want to provide a fake alternative that does what you want it to do. I'll try and provide a good example. I use Moq, but you can choose whatever mocking framework you like.</p> <p>In this test, I simply assert that Subscribe was called in the constructor, but your test might be more complicated if you are wanting to test the class's reaction to a raised event. The test shows a <code>CompositePresentationEvent<int></code>.</p> <pre><code>//Arrange Mock<MyEvent> mockEvent = new Mock<MyEvent>(); Mock<IEventAggregator> mockAggregator = new Mock<IEventAggregator>(); mockEvent.Setup ( evnt => evnt.Subscribe(It.IsAny<Action<int>>()) ); mockAggregator.Setup ( agg => agg.GetEvent<MyEvent>() .Returns(mockEvent.Object); ); //Act MyClassIWantToTest target = new MyClassIWantToTest(mockAggregator.Object); //Assert mockEvent.VerifyAll(); </code></pre> <p>That's the basics. The rule of thumb here is that if you tests rely on a system resource that is difficult to provide, isolate it from the test.</p> <p><strong>Edit: after reading your question I see you are trying to test the callback.</strong> </p> <p>In this sample, I test if the "CurrentValueProperty" property is set to whatever value is passed in the callback method. Here is that sample:</p> <pre><code>//Arrange Mock<MyEvent> mockEvent = new Mock<MyEvent>(); Mock<IEventAggregator> mockAggregator = new Mock<IEventAggregator>(); Action<int> theEventCallback = null; mockEvent.Setup ( evnt => evnt.Subscribe(It.IsAny<Action<int>>()) ) .Callback<Action<int>> ( cb => theEventCallback = cb ); mockAggregator.Setup ( agg => agg.GetEvent<MyEvent>() ) .Returns(mockEvent.Object); //Act MyClassIWantToTest target = new MyClassIWantToTest(mockAggregator.Object); //we expect this to be populated by the callback specified in our mock setup //that will be triggered when Subscribe is called in //MyClassIWantToTest's constructor theEventCallback(27); //Assert Assert.AreEqual(target.CurrentValueProperty, 27); </code></pre> <p>That's it.</p>

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