Bug: tests-depend-on-uncontrolled-environment #931

• Work Mode: full-bug

Summary

Consolidates #905 and #906. The shared root cause: a unit test depends on environment state it does not control, so its result depends on scheduling or on other processes rather than on the code under test.

1. Bug: Bug: Sibling breadcrumb dispatcher tests share the Task.Run distinct-thread assumption fixed in #900 #905: tests use Task.Run as the "other thread". Task.Run guarantees only a thread-pool thread, never a different one, so under parallel execution the guard under test can go unexercised. PR fix(quickfiler): run breadcrumb thread-affinity worker tests on a dedicated thread #904 (Bug: Bug: Breadcrumb thread-affinity tests assume Task.Run yields a distinct thread #900) fixed two instances. Remaining:
   • QuickFiler.Test/Viewers/ItemViewerBreadcrumbThreadAffinityTests.cs:332. The file is 490 lines, so the fix requires a split to stay under 500.
   • Candidates to triage:
     • BreadcrumbSelectorToggleUiBoundaryTests.cs:75
     • BreadcrumbPopupControlDispatchTests.cs:29,111
     • BreadcrumbPopupBoundaryCoverageTests.cs:58
     • BreadcrumbPopupBoundaryCoverageTests.Part2.cs:192
     • BreadcrumbUiThreadDispatchTests.cs:90,301
   • Task.Run(() => tcs.SetResult(...)) calls that only complete a task are not affected.
2. Bug: Bug: FileInfoWrapper_Tests.OpenRead opens the repository's own TaskMaster.sln #906: UtilitiesCS.Test/HelperClasses/FileInfoWrapper_Tests.cs:56-62 opens the repository's own TaskMaster.sln, found by GetSolutionFile() at lines 340-352, as a fixture. Resident MSBuild node-reuse workers can hold that file open, so the outcome depends on build history.

Environment

• OS/version: Windows 11 Pro 10.0.26200
• Python version: not applicable (C#, MSTest, net48)
• Command/flags used: parallel regime /Settings:TaskMaster.runsettings (Workers 0, Scope ClassLevel)
• Data source or fixture: files listed above, main at 177b6d78e

Steps to Reproduce

1. Inspect the cited Task.Run sites and confirm that each asserts a thread-identity property against the thread it obtained.
2. Inspect FileInfoWrapper_Tests.GetSolutionFile() and confirm it resolves the repository's own solution file.

Expected Behavior

• A test that needs a distinct thread uses a dedicated Thread that is joined, and asserts inside that thread that it is distinct (for example CheckAccess() == false) before exercising the guard. This is the Bug: Bug: Breadcrumb thread-affinity tests assume Task.Run yields a distinct thread #900 pattern.
• A file-handle test uses a stream the test owns, supplied through the wrapper's seam or an in-memory stream. It never uses a repository file.
• Temporary files are prohibited by the unit-test policy and must not be used.

Actual Behavior

The guard under test can pass without being exercised, and the file-open test can fail or pass depending on MSBuild worker residency.

Logs / Screenshots

• Attached minimal logs or screenshot
• Snippet: none (static findings, verified present on 2026-09-28)

Impact / Severity

• Blocker
• High
• Medium
• Low

Source

From: docs/features/potential/2026-09-28-tests-depend-on-uncontrolled-environment.md