Bug: utilitiescs-test-determinism-780-803-594

[drmoisan]

• Work Mode: full-bug

Summary

Consolidates the UtilitiesCS.Test nondeterminism filed as #780, #803, and #594 into one item so the required mstest-coverage check stops failing on unrelated pull requests. #803 is a duplicate of the DfDeedle_COM_Tests NullReferenceException already in #594: GetEmailDataInViewAsync_SeparatesTableSnapshotFromDataFrameTransform fails under parallel load because the class mutates static seams and production code at DfDeedle.cs:186 dereferences tableSnapshot.Item1 without a null check. #780 is DictionaryExtensions.TryAddValuesAsync cancelling its inner Task.Run after a hard-coded 500 ms wall-clock window, which the thread pool exceeds under coverage instrumentation with 24 class workers. #594 also carries two Console.Out races between concurrently executing tests. #592 (QuickFiler pump-host 60 s expiry) is deliberately not included: it is a different assembly and needs its own investigation.

Environment

• OS/version: Windows 11 Pro 10.0.26200 locally; GitHub Actions windows runner in CI
• Runtime: .NET Framework 4.8.1 test host, VSTest 18.9.0, MSTest 4.4.0, assembly-level parallelization with 24 class-scope workers
• Command/flags used: vstest.console.exe <nine assemblies> /EnableCodeCoverage /InIsolation /Logger:trx "/TestCaseFilter:TestCategory!=LiveOutlook"; the repository mstest-coverage job
• Data source or fixture: in-memory dictionaries; mocked Table and MAPIFolder in DfDeedle_COM_Tests

Steps to Reproduce

1. Run the full suite under coverage with parallel class workers. Observe, intermittently: TryAddValuesAsync_UpdatesExistingValue failing with TaskCanceledException after ~20 s (passes in ~2 ms alone); GetEmailDataInViewAsync_SeparatesTableSnapshotFromDataFrameTransform failing with NullReferenceException at DfDeedle.cs:186; two Console.Out races.
2. Re-run the identical head commit with no change and observe all checks passing. Observed on PR bug(799): render breadcrumb lineage below the archive root and unify suggestion-path projection #802 at b2132349 (7107 of 7108 passed, then green on re-run) and during PR Chore/update dependencies #779 verification on 2026-09-04.

Expected Behavior

• Every test in UtilitiesCS.Test passes deterministically regardless of class ordering and parallel load.
• TryAddValuesAsync does not fail production callers on thread-pool scheduling latency.
• Production code at DfDeedle.cs:186 does not dereference a possibly-null snapshot element.
• A full nine-assembly /InIsolation run reports zero failures on ten consecutive runs.

Actual Behavior

Intermittent failures as above, each blocking a required check on an unrelated pull request and inviting re-run-until-green.

Logs / Screenshots

• Attached minimal logs or screenshot
• Snippet (Bug: tryaddvaluesasync-wall-clock-timeout-flaky #780, 2026-09-04): System.Threading.Tasks.TaskCanceledException: A task was canceled. at UtilitiesCS.DictionaryExtensions.<TryAddValuesAsync>d__10\2.MoveNext() in UtilitiesCS\Extensions\DictionaryExtensions.cs:line 179`. Local run 4767 tests, 4766 passed, the failing test alone took 21 s.
• Snippet (Bug: dfdeedle-com-tests-static-seam-race-under-parallel-load #803, PR bug(799): render breadcrumb lineage below the archive root and unify suggestion-path projection #802 run 1): System.NullReferenceException at UtilitiesCS.DfDeedle.GetEmailDataInViewAsync, UtilitiesCS/Extensions/DfDeedle.cs line 186, Total 7108, Passed 7107, Failed 1.

Impact / Severity

• Blocker
• High
• Medium
• Low

Medium: a nondeterministic failure in a required check blocks unrelated pull requests and erodes the signal the gate exists to provide. Production callers of TryAddValuesAsync may also receive a spurious cancellation under starvation.

Source

From: docs/features/potential/2026-09-07-utilitiescs-test-determinism-780-803-594.md