FakeTimeProvider.Advance fails to advance delays (at least in the case of Polly)

[rcollette]

Description

When using FakeTimerProvider in unit tests, retries configured in a ResiliencyPipeline are not executed.

The library maintainer believes the issue lies in FakeTimerProvider
App-vNext/Polly#1932

Reproduction Steps

Please see the minimal unit test repo
https://github.com/rcollette/PollyRetryFakeTimeProviderIssue

Expected behavior

Delays used in Poly should be advanced.

Actual behavior

They don't appear to be triggered.

Regression?

No response

Known Workarounds

No response

Configuration

.NET 8.0.101
Polly 8.2.1

Other information

I tried to debug down into the WakeWaiters/InvokeCallback/TimerCallback code but was not seeing why this was not triggering.

[dariusclay]

@geeknoid @martintmk So the issue here can be resolved in unit tests by ensuring that awaited tasks which need to be advanced by the time provider are configured with ConfigureAwait(true) to ensure execution continues on the captured context. Polly provides a way to pass in the ResilienceContext to use this behavior.

[dariusclay]

@rcollette if you use the below code to execute the pipeline, the tests will succeed. Continuing on captured context is important here in the unit tests so that advancing the time synchronizes with the delays in the ExecuteAsync task.

    public async Task<int> PollyRetry(double taskDelay, double cancellationSeconds)
    {
        CancellationTokenSource cts = new(TimeSpan.FromSeconds(cancellationSeconds), timeProvider);
        Tries = 0;

        // get a context from the pool and return it when done
        var context = ResilienceContextPool.Shared.Get(
            // ensure execution continues on captured context 
            continueOnCapturedContext: true, 
            cancellationToken: cts.Token);

        var result = await _retryPipeline.ExecuteAsync(
            async _ =>
            {
                Tries++;

                // Simulate a task that takes some time to complete
                await Task.Delay(TimeSpan.FromSeconds(taskDelay), timeProvider);

                if (Tries <= 2)
                {
                    throw new InvalidOperationException();
                }

                return Tries;
            },
            context);

        ResilienceContextPool.Shared.Return(context);

        return result;
    }