Question

I’m dipping my toes in how to test multi-threaded stuff, but not quite sure how to get started. I’m sure I will figure more stuff out easier if I could just get stuff going, so I was wondering if someone could help me write an NUnit test case for this simple class:

class Worker
{
    public event EventHandler<EventArgs> Done = (s, e) => { };

    public void StartWork()
    {
        var thread = new Thread(Work) { Name = "Worker Thread" };
        thread.Start();
    }

    private void Work()
    {
        // Do some heavy lifting
        Thread.Sleep(500);
        Done(this, EventArgs.Empty);
    }
}

What I would like to test is simply: Is the Done event raised when it finishes. I would have no problems if it was synchronous, but not sure where to even begin when it is not. A simple test if it wasn’t multi-threaded (and the Work method wasn’t private) could be:

[TestFixture]
class WorkerTests
{
    [Test]
    public void DoWork_WhenDone_EventIsRaised()
    {
        var worker = new Worker();

        var eventWasRaised = false;
        worker.Done += (s, e) => eventWasRaised = true;

        worker.Work();
        Assert.That(eventWasRaised);
    }
}

Any pointers?

Answer 1

You need to use a ManualResetEvent – see Unit Testing Multi-Threaded Asynchronous Events for more details.

Something like:

[Test]
public void DoWork_WhenDone_EventIsRaised()
{
   var worker = new Worker();

   var eventWasRaised = false;
   var mre = new ManualResetEvent(false);
   worker.Done += (s, e) => { eventWasRaised= true; mre.Set(); };

   worker.Work();
   mre.WaitOne(1000);
   Assert.That(eventWasRaised);
}