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POUnit Testing CompositePresentationEvent when using the Dispatcher
 

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    <p>Im using the Prism/Composite Application Library and trying to unit test some code that subscribes to a CompositePresentationEvent using the EventAggregator. The code that is raising the event is raising it on another thread so I am subscribing to the event using ThreadOption.UIThread.</p> <p>When the event raises the callback it uses the application dispatcher to put it onto the UI thread. This is fine during normal execution but during a unit test there is no dispatcher. The code in CompositePresentationEvent looks like this:</p> <pre><code> private IDispatcherFacade UIDispatcher { get { if (uiDispatcher == null) { this.uiDispatcher = new DefaultDispatcher(); } return uiDispatcher; } } public class DefaultDispatcher : IDispatcherFacade { /// &lt;summary&gt; /// Forwards the BeginInvoke to the current application's &lt;see cref="Dispatcher"/&gt;. /// &lt;/summary&gt; /// &lt;param name="method"&gt;Method to be invoked.&lt;/param&gt; /// &lt;param name="arg"&gt;Arguments to pass to the invoked method.&lt;/param&gt; public void BeginInvoke(Delegate method, object arg) { if (Application.Current != null) { Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal, method, arg); } } } </code></pre> <p>The problem being that CompositePresentationEvent is tied to the DefaultDispatcher, and this dispatcher does nothing if there is no Application running.</p> <p>Has anyone had any success unit testing in this kind of situation? Any tips or workarounds to kick the dispatcher into life?</p> <p>I know I could make my callback internal and allow my unit test to call this method but I would prefer not to change my code and leave this approach as a last resort.</p>
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    1. COif you're trying to unit-test your class (not `CompositePresentationEvent`) then introducing real `CompositePresentationEvent` instance in your test makes them non-unit. Maybe instead of playing with CPE you should isolate your class from it and then use mocks/stubs?
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    2. COYes fair point. I think I got a bit bogged down in the problems presented by these classes when I should be able to mock them out. I will try andersons suggestion and see if it resolves it. Thanks!
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