How do I prevent by Rx test from hanging?

Question

I am reproducing my Rx issue with a simplified test case below. The test below hangs. I am sure it is a small, but fundamental, thing that I am missing, but can't put my finger on it.

   public class Service
   {
        private ISubject<double> _subject = new Subject<double>();
        public void Reset()
        {
            _subject.OnNext(0.0);
        }

        public IObservable<double> GetProgress()
        {
            return _subject;
        }
    }

    public class ObTest
    {
        [Fact]
        private async Task SimpleTest()
        {
            var service = new Service();

            var result = service.GetProgress().Take(1);

            var task = Task.Run(async () =>
            {
                service.Reset();
            });

            await result;
        }
    }

UPDATE

My attempt above was to simplify the problem a little and understand it. In my case GetProgress() is a merge of various Observables that publish the download progress, one of these Observables is a Subject<double> that publishes 0 everytime somebody calls a method to delete the download.

The race condition identified by Enigmativity and Theodor Zoulias may(??) happen in real life. I display a view which attempts to get the progress, however, quick fingers delete it just in time.

What I need to understand a bit more is if the download is started again (subscription has taken place by now, by virtue of displaying a view, which has already made the subscription) and somebody again deletes it.

   public class Service
   {
        private ISubject<double> _deleteSubject = new Subject<double>();
        public void Reset()
        {
            _deleteSubject.OnNext(0.0);
        }

        public IObservable<double> GetProgress()
        {
            return _deleteSubject.Merge(downloadProgress);
        }
    }

Answer 1

Your code isn't hanging. It's awaiting an observable that sometimes never gets a value.

You have a race condition.

The Task.Run is sometimes executing to completion before the await result creates the subscription to the observable - so it never sees the value.

Try this code instead:

private async Task SimpleTest()
{
    var service = new Service();

    var result = service.GetProgress().Take(1);

    var awaiter = result.GetAwaiter();

    var task = Task.Run(() =>
    {
        service.Reset();
    });

    await awaiter;
}