C#/.NET: Testing BackgroundWorker with NUnit

Question

This test fails when it is run with the NUnit console runner. It works if I run just that test with TestDriven.NET, but not if I run the entire suite with TestDriven.NET:

[Test]
public void BackgroundWorkerFiresRunWorkerCompleted()
{
  var runner = new BackgroundWorker();
  ManualResetEvent done = new ManualResetEvent(false);
  runner.RunWorkerCompleted += delegate { done.Set(); };

  runner.RunWorkerAsync();

  bool res = done.WaitOne(TimeSpan.FromSeconds(10));
  // This assert fails:
  Assert.IsTrue(res, "RunWorkerCompleted was not executed within 10 seconds");
}

I suspect the problem have something to do with not having a message-loop, but I am not sure.

What are the requirements for using BackgroundWorker?

Is there a workaround to make the test work?

Answer 1

Are you missing a BGW DoWork event handler?

Answer 2

I don't think that it has to do with the message pump, since tests usually run in a blocking fashion anyways. But it may be that the event is invoked on the "UI" thread, which uses a windows message which does not get handled.

So, if the problem was the message pump or windows messages not being handled, you could try like this to replace your current bool res = done.WaitOne(TimeSpan.FromSeconds(10)); line:

DateTime end = DateTime.Now.AddSeconds(10);
bool res = false;
while ((!res) && (DateTime.Now<end)) {
   Application.DoEvents();
   res = done.WaitOne(0):
}