Building unit tests for MVC2 AsyncControllers

Question

I\'m considering re-rewriting some of my MVC controllers to be async controllers. I have working unit tests for these controllers, but I\'m trying to understand how to maintain

Answer 1

As with any async code, unit testing needs to be aware of thread signalling. .NET includes a type called AutoResetEvent which can block the test thread until an async operation has been completed:

public class MyAsyncController : Controller
{
  public void TransactionAsync()
  {
    AsyncManager.Parameters["result"] = "result";
  }

  public ContentResult TransactionCompleted(string result)
  {
    return Content(result);
  }
}

[TestFixture]
public class MyAsyncControllerTests
{
  #region Fields
  private AutoResetEvent trigger;
  private MyAsyncController controller;
  #endregion

  #region Tests
  [Test]
  public void TestTransactionAsync()
  {
    controller = new MyAsyncController();
    trigger = new AutoResetEvent(false);

    // When the async manager has finished processing an async operation, trigger our AutoResetEvent to proceed.
    controller.AsyncManager.Finished += (sender, ev) => trigger.Set();

    controller.TransactionAsync();
    trigger.WaitOne()

    // Continue with asserts
  }
  #endregion
}

Hope that helps :)

Answer 2

I've written short AsyncController extension method that simplifies unit testing a bit.

static class AsyncControllerExtensions
{
    public static void ExecuteAsync(this AsyncController asyncController, Action actionAsync, Action actionCompleted)
    {
        var trigger = new AutoResetEvent(false);
        asyncController.AsyncManager.Finished += (sender, ev) =>
        {
            actionCompleted();
            trigger.Set();
        };
        actionAsync();
        trigger.WaitOne();
    }
}

That way we can simply hide threading 'noise':

public class SampleAsyncController : AsyncController
{
    public void SquareOfAsync(int number)
    {
        AsyncManager.OutstandingOperations.Increment();

        // here goes asynchronous operation
        new Thread(() =>
        {
            Thread.Sleep(100);

            // do some async long operation like ... 
            // calculate square number
            AsyncManager.Parameters["result"] = number * number;

            // decrementing OutstandingOperations to value 0 
            // will execute Finished EventHandler on AsyncManager
            AsyncManager.OutstandingOperations.Decrement();
        }).Start();
    }

    public JsonResult SquareOfCompleted(int result)
    {
        return Json(result);
    }
}

[TestFixture]
public class SampleAsyncControllerTests
{
    [Test]
    public void When_calling_square_of_it_should_return_square_number_of_input()
    {
        var controller = new SampleAsyncController();
        var result = new JsonResult();
        const int number = 5;

        controller.ExecuteAsync(() => controller.SquareOfAsync(number),
                                () => result = controller.SquareOfCompleted((int)controller.AsyncManager.Parameters["result"]));

        Assert.AreEqual((int)(result.Data), number * number);
    }
}

If you want to know more I've written a blog post about how to Unit test ASP.NET MVC 3 asynchronous controllers using Machine.Specifications Or if you want to check this code it's on a github