Unit Testing Multi-Threaded Asynchronous Events

I recently developed a stress/load testing tool. One of the classes implemented the Event-based Asynchronous Pattern. A good unit test for this class would be that the event is raised when expected (or at all). I found some posts on how to test events using NUnit. However, I did not see anything directly addressing the multi-threaded asynch event pattern. The following unit test uses an anonymous method and the ManualResetEvent to verify that the RunCompleted event fires after the call to RunAsync.

[Test()]
public void AfterRunAsync()
{
    ManualResetEvent manualEvent = new ManualResetEvent(false);

    TestTestCase tc = new TestTestCase(1, "", 0, 0);
    bool eventFired = false;
    tc.RunCompleted +=
        delegate(object sender, AsyncCompletedEventArgs e) {
            Assert.IsInstanceOfType(typeof (TestTestCase), sender, "sender is TestCase");
            bool passed = tc.Passed;
            string output = tc.Output;
            eventFired = true;
            manualEvent.Set();
        };
    tc.RunAsync();
    manualEvent.WaitOne(500, false);
    Assert.IsTrue(eventFired, "RunCompleted fired");
}
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4 Responses to “Unit Testing Multi-Threaded Asynchronous Events”

  1. Chris Says:

    Thanks, this really helped me out… I knew it had to be possible, but wasn’t connecting the dots ’til I read this.

  2. Andrew Dedman Says:

    Thanks very much John, This was very useful.

  3. Unit testing multi-threaded, asynchronous code and/or events | David's Blog Says:

    […] ManualResetEvent class (MSDN) seems a good choice for this, and this post has a small example of using it in a unit test: [Test()] public void AfterRunAsync() { […]

  4. Sheik Mohamed Says:

    Really excellent . its work for me.


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