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. — Waescher
– Waescher, Commented Jun 22, 2023 at 14:21

Waescher · Accepted Answer · 2023-06-22 14:30:48Z

0

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
}

answered Jun 22, 2023 at 14:30

Waescher

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