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POHow do I unit test a method containing an asynchronous call?
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  1. POHow do I unit test a method containing an asynchronous call?
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    copied!<p>I have a method that contains an asynchronous call like this:</p> <pre><code>public void MyMethod() { ... (new Action&lt;string&gt;(worker.DoWork)).BeginInvoke(myString, null, null); ... } </code></pre> <p>I'm using Unity and creating mock objects is not a problem, but how can I test that DoWork is called without worrying about race conditions?</p> <p>A <a href="https://stackoverflow.com/questions/400552/what-is-the-best-way-to-unit-test-an-asynchronous-method">previous question</a> offers a solution, but it seems to me that wait-handles is a hack (the race condition is still there, although it should be virtually impossible to raise).</p> <hr> <p>EDIT: Okay, I thought I could ask this question in a very general manner, but it seems I have to elaborate further on the problem:</p> <p>I want to create a test for the above mentioned MyMethod, so I do something like this:</p> <pre><code>[TestMethod] public void TestMyMethod() { ...setup... MockWorker worker = new MockWorker(); MyObject myObj = new MyObject(worker); ...assert preconditions... myObj.MyMethod(); ...assert postconditions... } </code></pre> <p>The naïve approach would be to create a MockWorker() that simply sets a flag when DoWork has been called, and test that flag in the postconditions. This would of course lead to a race condition, where the postconditions are checked before the flag is set in the MockWorker.</p> <p>The more correct approach (which I'll probably end up using) is using a wait-handle:</p> <pre><code>class MockWorker : Worker { public AutoResetEvent AutoResetEvent = new AutoResetEvent(); public override void DoWork(string arg) { AutoResetEvent.Set(); } } </code></pre> <p>...and use the following assertion:</p> <pre><code>Assert.IsTrue(worker.AutoResetEvent.WaitOne(1000, false)); </code></pre> <p>This is using a semaphore-like approach, which is fine... but in <em>theory</em> the following could happen:</p> <ol> <li>BeginInvoke is called on my DoWork delegate</li> <li>For some reason neither the main-thread or the DoWork-thread is given execution time for 1000ms.</li> <li>The main-thread is given execution time, and because of the timeout the assertion fails, even though the DoWork thread is yet to be executed.</li> </ol> <p>Have I misunderstood how AutoResetEvent works? Am I just being too paranoid, or is there a clever solution to this problem?</p>
 

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