Why does NUnit lose its SynchronizationContext after await?

Question

Why does this test fail?

[Test]
public async Task Test_Keeps_SynchronizationContext()
{
    SynchronizationContext.Current.Should().NotBeNull(); // OK
    await Task.Delay(1).ConfigureAwait(true);
    SynchronizationContext.Current.Should().NotBeNull(); // FAIL
}

(NUnit 3.13.3 on .NET 7.0)

I read a few posts around NUnit and SynchronizationContexts (which did not match exactly) and I thought that maybe there is something I seem to overlook. But yes, I see this is pretty specific so I just created an [issue on GitHub](https://github.com/nunit/nunit/issues/4407). — Waescher, Jun 22 '23 at 14:21

score 0 · Answer 1 · answered Jun 22 '23 at 14:30

I found out that this is just the case for multi-threaded apartments. To fix this and keep the SynchronizationContext, you'll need to enter a single-threaded apartment by adding the ApartmentAttribute:

[Test, Apartment(ApartmentState.STA)]
public async Task Test_Keeps_SynchronizationContext()
{
    SynchronizationContext.Current.Should().NotBeNull(); // OK
    await Task.Delay(1).ConfigureAwait(true);
    SynchronizationContext.Current.Should().NotBeNull(); // OK
}

Why does NUnit lose its SynchronizationContext after await?

1 Answers1