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[mutation-test-improver] Monthly Report 2026-10

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Refactor
Clarity
Needs clarification
Activity status
Active
Tech stack
csharp
Domain
testing-qa

Research direction

Start with stryker-config.json and the latest successfully parsed mutation report, then inspect Client/MtpServerInProcessHost.cs and ../Microsoft.Testing.Platform/ServerMode/JsonRpc/RpcIdParser.cs. Use the linked mutation-testing workflow and run history to reproduce the listed survivors and no-coverage mutants. Done means addressing a selected hotspot and confirming the next parsed report shows the expected improvement.

Written by the indexing model from the issue text.

Description

type/automation type/test-gap

Mutation Testing Report for October 2026

Suggested Actions for Maintainer

  • Investigate survived hotspot Client/MtpServerInProcessHost.cs: 34 survived, 15 no-coverage mutants as of the last successfully parsed run, none auto-fixed yet - View report
  • Investigate survived hotspot ../Microsoft.Testing.Platform/ServerMode/JsonRpc/RpcIdParser.cs: 23 survived, 29 no-coverage mutants as of the last successfully parsed run - View report

(Exclude items already checked off by the maintainer in a previous edition, and anything closed/merged. If nothing needs attention, state "No suggested actions at this time.")

Score Trend

Date Score Killed Survived No Coverage Timeout Δ vs previous
2026-09-28 23.76% 349 270 1325 148 +0.12 pts
2026-09-24 23.64% 346 273 1326 149 +1.55 pts
2026-09-23 22.09% 313 296 1326 147 +0.19 pts
2026-09-22 21.90% 308 300 1326 148 n/a (first successful run)

(Keep the most recent ~14 rows; drop older ones - full history remains in Run History below.)

Top Survived-Mutant Hotspots

Ranked by Survived + NoCoverage count (Stryker scope: server-mode client sources, see stryker-config.json), carried forward from the last successfully parsed run (2026-09-28, run 36380741851) since no newer run has produced a parseable artifact:

  1. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/SerializerUtilities.TestNodeSerializers.cs — S=11, NC=126
  2. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Json.TestNodeSerializer.cs — S=7, NC=103
  3. ../Microsoft.Testing.Platform/Messages/TestCoverageMessages.cs — S=0, NC=97
  4. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/RpcMessages.cs — S=1, NC=90
  5. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Json.Deserializers.cs — S=18, NC=67
  6. ../Microsoft.Testing.Platform/Messages/PropertyBag.cs — S=4, NC=70
  7. ../Microsoft.Testing.Platform/Messages/TestNodeStateProperties.cs — S=0, NC=72
  8. ../Microsoft.Testing.Platform/Messages/TimingProperties.cs — S=0, NC=66
  9. ../Microsoft.Testing.Platform/Messages/FileLocationProperties.cs — S=0, NC=56
  10. Client/MtpServerClient.cs — S=18 (2 killed via merged PR #11587), NC=35
  11. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/RpcIdParser.cs — S=23, NC=29
  12. ../Microsoft.Testing.Platform/Messages/TestMethodIdentifierProperty.cs — S=0, NC=50
  13. Client/MtpServerInProcessHost.cs — S=34, NC=15
  14. ../Microsoft.Testing.Platform/Helpers/TaskExtensions.cs — S=0, NC=46
  15. ../Microsoft.Testing.Platform/ServerMode/JsonRpc/TcpMessageHandler.cs — S=33, NC=12

CompileError mutants (611 total, mostly in generated/serializer safe-mode paths) and RuntimeError/Timeout mutants are tracked separately and excluded from this hotspot ranking.

Known Equivalent Mutants

None recorded yet.

Run History

2026-10-11 05:02 UTC - Run
  • ⚠️ Run failed/cancelled - no report available. The run failed at the "Validate mutation testing configuration" step (a Python unit test asserting the mutation-testing module manifest covers every MTP extension project), before any module's "Mutate" or "Aggregate" job started. No mutation-testing-report artifact was produced (0 artifacts on the run). No open mutation-test-improver PRs required reconciliation this run. Retained the last successfully parsed run's figures above (run 36380741851, 2026-09-28).
2026-10-04 06:53 UTC - Run
  • ⚠️ Run failed/cancelled - no report available. The run's conclusion was failure and only the mutation-testing-full-report (HTML summary) artifact was published, not the mutation-testing-report data artifact required for parsing mutants. No module-result.json was available to confirm a successful ServerMode module within the failed aggregate. No open mutation-test-improver PRs or pending-PR entries required reconciliation this run. Retained the last successfully parsed run's figures above (run 36380741851, 2026-09-28).
2026-10-02 06:26 UTC - Run
  • ⚠️ Report artifact could not be parsed this run: downloading the mutation-testing-report artifact (via gh run download and via direct gh api .../artifacts/<id>/zip) produced a 1,338,067-byte file for a 738,620-byte source archive, with 306,716 occurrences of the UTF-8 replacement character U+FFFD injected into the binary stream — the same irreversible binary-to-text corruption in the proxy path observed on 2026-09-30. No fresh score/hotspot data available; retained the last successfully parsed run's figures above (run 36380741851, 2026-09-28). No open mutation-test-improver PRs or pending-PR entries required reconciliation this run — all prior fixes (#11450, #11587) are merged.
2026-09-28 06:20 UTC - Run
  • Score: 23.76% (Killed 349 / Survived 270 / No Coverage 1325 / Timeout 148)
  • ✅ Merged PR #11587: killed 2 survived String mutation mutants in Client/MtpServerClient.cs:219 (unsupported-protocol-version message)
  • 🟰 No fix attempted for the MtpServerInProcessHost.cs hotspot this run (the 2-run Stryker verification budget was spent confirming the MtpServerClient.cs fix)
2026-09-24 06:23 UTC - Run
  • Score: 23.64% (Killed 346 / Survived 273 / No Coverage 1326 / Timeout 149)
  • 🟰 No fix opened this run: investigated MtpServerClient.RaiseLog/RaiseTelemetry/RaiseAttachments's @params is null || handler is null guard mutants (||→&&). Abandoned due to test-harness flakiness in event ordering; reverted edits.
2026-09-23 06:23 UTC - Run
  • Score: 22.09% (Killed 313 / Survived 296 / No Coverage 1326 / Timeout 147)
  • ✅ Merged PR #11450: killed 5 survived boolean-default mutants in Client/MtpServerClient.cs:316-320 (capability-flag defaults)
2026-09-22 06:12 UTC - Run
  • Score: 21.90% (Killed 308 / Survived 300 / No Coverage 1326 / Timeout 148)
  • 🕒 Pending PR creation (reconciled 2026-09-23 as merged PR #11450): verified fix for mutant in Client/MtpServerClient.cs:316-320 (5 boolean-default mutants)

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