test(InProcessTestHost): external-event + durable-timer timeout coverage (relates to #713)

[YunchuWang]

Summary

Adds InProcessTestHost.Tests coverage for external events (TaskOrchestrationContext.WaitForExternalEvent<T>), including the canonical Task.WhenAny(eventTask, timerTask) "wait for an event with a timeout" pattern. This fills a gap in external-event test coverage and documents the correct durable-timer cancellation semantics.

Relates to #713.

Background — #713 is expected behavior

#713 reports that an orchestration awaiting Task.WhenAny(externalEventTask, timerTask) appears to "hang" after the external event is raised, while the durable timer is still pending.

A verification-only investigation shows the external event is delivered and wins the WhenAny. The orchestration does not complete because a durable timer that was created but never cancelled remains outstanding. This is standard Durable Task Framework behavior, already documented on TaskOrchestrationContext.CreateTimer:

All durable timers created using this method must either expire or be cancelled using the cancellationToken before the orchestrator can complete. If unexpired timers exist when the orchestration completes, it will remain in the "Running" state until the scheduled expiration time.

and on Microsoft Learn (durable-functions-timers): the framework doesn't change an orchestration's status to Completed until all outstanding tasks, including durable timer tasks, are either completed or canceled.

The issue's repro uses a 5-minute timer and never cancels it, so the instance stays Running until the timer would fire (~5 min) — which looks like a hang inside a short test. This is not a lost/dropped event and not an InProcessTestHost-specific defect: the worker forwards the CancellationToken straight into DurableTask.Core (TaskOrchestrationContextWrapper.CreateTimer), the same path all backends use.

What this PR adds

test/InProcessTestHost.Tests/ExternalEventTests.cs with three fast, deterministic tests:

1. WaitForExternalEvent_IsDelivered — a plain external event is delivered to a waiting orchestration and its payload is returned (fills the missing plain external-event coverage).
2. WaitForExternalEvent_WithTimeout_EventWins — the canonical pattern: a 5-minute timer under Task.WhenAny; when the event wins, the timer's CancellationTokenSource is cancelled so the orchestration completes promptly (well under the timer) with the event payload.
3. WaitForExternalEvent_WithTimeout_TimerWins — same shape with a short 2 s timer and no event raised; the timer wins and the orchestration returns "timeout".

Each test uses a 30 s completion CancellationTokenSource purely as a safety guard; all complete in a few seconds.

Notes

• No runtime/product code changes. The CreateTimer cancellation/completion semantics are already documented on the public API, so this PR only adds tests (with a summary comment in the test file pointing at those docs). It does not change observable behavior.
• Does not close InMemoryOrchestrationService: External events not delivered when durable timer is pending in Task.WhenAny #713 — filed as Relates to, since the reported behavior is by design; these tests document the correct usage pattern.

Validation

dotnet test test/InProcessTestHost.Tests/InProcessTestHost.Tests.csproj -c Debug -f net10.0 → 22 passed, 0 failed (3 new tests + 19 existing).

[Copilot]

Pull request overview

Adds new InProcessTestHost.Tests coverage for external event delivery (TaskOrchestrationContext.WaitForExternalEvent<T>), including the common “external event with durable-timer timeout” Task.WhenAny pattern described in #713, to document correct completion/cancellation behavior in the in-process test host.

Changes:

• Added a new test suite validating basic external-event delivery.
• Added timeout-pattern tests covering both “event wins” and “timer wins” branches.
• Included remarks in the test file that point to the durable-timer cancellation requirement documentation.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.