perf: use GetUpperCaseName in InternalSyncLog to avoid Enum.ToString() allocation

[Evangelink]

Fixes #10261

What

FileLogger.InternalSyncLog interpolated {logLevel} directly, which calls Enum.ToString() — boxing the enum and allocating a fresh string for every log line written on the sync-flush path.

The async/enqueue paths already go through BuildLogEntry → GetUpperCaseName, which returns an interned literal ("TRACE", "WARNING", …) with zero allocation. This applies the same helper to the sync path.

Behavior change

The level in the sync-flush diagnostic log now renders upper-cased ([00:00:00.000 Test - TRACE] … instead of - Trace]), matching the async path. Everything else — including the sync path's HH:mm:ss.fff timestamp format — is unchanged.

Tests

• Updated the two existing sync-path assertions to expect the upper-cased level.
• Added Log_WhenSyncFlush_LogLevelIsWrittenInUpperCase (data-driven over the existing exhaustive ExpectedUpperCaseNames table) and Log_WhenSyncFlush_UndefinedLogLevelIsWrittenAsItsNumericValue, mirroring the async-path coverage so the sync formatter no longer relies on the async tests for level rendering.

Microsoft.Testing.Platform.UnitTests — 127/127 passing on net9.0.

[Copilot]

Pull request overview

Optimizes synchronous file logging by avoiding Enum.ToString() allocations and aligning log-level casing with asynchronous logging.

Changes:

• Uses GetUpperCaseName in the synchronous logging path.
• Updates existing expectations and adds exhaustive sync-path coverage.

Show a summary per file

File	Description
src/Platform/Microsoft.Testing.Platform/Logging/FileLogger.cs	Uses allocation-free uppercase names for known log levels.
test/UnitTests/Microsoft.Testing.Platform.UnitTests/Logging/FileLoggerTests.cs	Verifies uppercase and undefined log-level formatting.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Medium

[github-actions]

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

Review Summary

Clean, well-scoped performance fix. No issues found.

Verdict Table

#	Dimension	Verdict
1	Algorithmic Correctness	✅ GetUpperCaseName is a pure switch expression already used by the async path; applying it to the sync path is trivially correct.
2	Edge Cases & Defensive Coding	✅ Undefined enum values fall through to ToString().ToUpper() — tested by new UndefinedLogLevelIsWrittenAsItsNumericValue test.
3	Concurrency & Thread Safety	✅ N/A — no change to locking; _semaphore still guards the sync path.
4	Performance & Allocations	✅ This is the fix — eliminates Enum.ToString() boxing + allocation per sync log line.
5	API Design & Public Surface	✅ N/A — no public API change; GetUpperCaseName is private static.
6	Backward Compatibility	✅ Behavior change (upper-case level name in sync logs) is intentional and aligns sync with async output. Diagnostic log format is not a public contract.
7	Error Handling	✅ N/A — no change to error paths.
8	Cross-TFM Correctness	✅ N/A — changed line is outside any #if block.
9	Resource Management	✅ N/A.
10	Nullability & Type Safety	✅ N/A.
11	Naming & Readability	✅ Clear.
12	Test Quality	✅ New tests mirror the async-path coverage (DynamicData over all levels + undefined value). Good use of SyncFlushDefaultClockTimestamp constant and LogSingleEntryWithSyncFlush helper.
13	Test Conventions	✅ Uses MSTest Assert, consistent with BannedSymbols.txt for this project.
14	Localization	N/A — no resource string changes.
15	Security	N/A.
16	IPC & Serialization	N/A.
17	Configuration & Options	N/A.
18	Logging & Diagnostics	✅ The logging output format is the subject of the fix; both paths now agree.
19	MSBuild & Packaging	N/A.
20	Documentation	✅ Inline comments on the new constant and tests are helpful.
21	Scope Discipline	✅ Single-concern PR with matching issue reference.
22	PublicAPI.Unshipped.txt	✅ N/A — no public API additions.

Result: All clear. No blocking or non-blocking issues identified.

[github-actions]

🧪 Test quality grade — PR #10265

Grade	Test	Mutation	Notes	How to improve
B (80–89)	mod FileLoggerTests. Write_ IfMalformedUTF8_ ShouldNotCrash	2/3 killed	Partial-match assertions (StartsWith/EndsWith) leave the timestamp format and full entry structure unchecked; intentional because a real clock is used.	Inject a mock clock and switch to Assert.AreEqual with the full expected string to kill timestamp-format mutations.
A (90–100)	mod FileLoggerTests. Log_ WhenSyncFlush_ StreamWriterIsCalledOnlyWhenLogLevelAllowsIt	4/4 killed	Exact string match for the enabled path and a length check for the disabled path cover all meaningful mutations; oracle uses ToUpperInvariant rather than independent literals but the level-gating intent is fully verified.	—
A (90–100)	new FileLoggerTests. Log_ WhenSyncFlush_ LogLevelIsWrittenInUpperCase	4/4 killed	Independent hardcoded oracle (ExpectedUpperCaseNames) prevents the test from passing if GetUpperCaseName regresses; all 7 named levels covered as separate data rows.	—
A (90–100)	new FileLoggerTests. Log_ WhenSyncFlush_ UndefinedLogLevelIsWrittenAsItsNumericValue	4/4 killed	Exact match for the switch-fallback branch with an out-of-range value; console-no-write check prevents silent rerouting.	—

_{This advisory comment was generated automatically. Grades are heuristic
and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · sonnet46 55.5 AIC · ⌖ 5.84 AIC · ⊞ 10.3K · [◷]( · ◷)