Forward generic warning/error host messages over the dotnet test pipe (protocol 1.3.0)

[Evangelink]

Context

Following up on #9463 (Azure DevOps logging-command forwarding), this continues closing the single-assembly ↔ dotnet test feature-parity gap.

Under the dotnet test pipe protocol the host installs a no-op output device (the SDK's TerminalTestReporter owns user-facing output), so the only host output that crossed the wire was test results, artifacts, session events, and — since #9463 — Azure DevOps logging commands. Every other host UI message was swallowed. That meant host-side diagnostics produced outside test results were lost in multi-assembly runs:

• HangDump diagnostics (timeout message, process tree, list of tests still running, disk info)
• CrashDump diagnostics ("process crashed", tests running at crash)
• Retry orchestrator summary ("failed attempt N/N+1", "completed after N attempts", explanations)
• Generic extension / framework warnings & errors (VSTestBridge MessageLoggerAdapter, adapter banners, custom extensions) — the broadest gap

What this does

Rather than special-casing each producer, this adds a generic pass-through channel and lets the client decide what to do with the messages.

Wire contract (shared with dotnet/sdk via ObjectFieldIds.cs + Constants.cs):

• Bumps ProtocolConstants.SupportedVersions → 1.0.0;1.1.0;1.2.0;1.3.0.
• New DisplayMessageFieldsId (serializer id 12) and DisplayMessageLevels (Information/Warning/Error).

Host side (this repo only):

• New DisplayMessage model + DisplayMessageSerializer (mirrors AzureDevOpsLogMessage).
• DotnetTestConnection: new IsDisplayMessageForwardingSupported (negotiated ≥ 1.3.0) + a SendMessageAsync case.
• DotnetTestPassthroughOutputDevice now forwards WarningMessageOutputDeviceData / ErrorMessageOutputDeviceData as DisplayMessage (gated on 1.3.0), alongside the existing Azure DevOps path. Informational text is still discarded (severity floor = Warning/Error).
• OutputDeviceManager now installs the forwarding device under the pipe protocol everywhere, not just on Azure DevOps agents (generic messages aren't AzDO-specific; the AzDO branch stays naturally inert off-agent).

The SDK-side sink already exists (TerminalTestReporter.WriteWarningMessage / WriteErrorMessage); only the transport was missing.

Design decisions

• Version-gated only — an older SDK that negotiates ≤ 1.2.0 never receives the new message id (host gates on the negotiated version). A finer-grained, handshake-negotiated type/severity filter is intentionally not added now (YAGNI for the current low message volume); the handshake stays an open dictionary so a WantedMessageSeverity knob can be added later without a protocol break.
• Severity-only, no color field to keep the wire minimal — forward-compatible to add later if needed.
• Kept AzureDevOpsLogMessage as its own path — it has a verbatim ##vso[...] pipeline-log requirement and is gated on the agent; folding it into DisplayMessage would change its semantics.

SDK follow-up (separate, like #9463)

dotnet/sdk needs its own DisplayMessage model/serializer copy and routing to the shared reporter's WriteWarningMessage/WriteErrorMessage. Not done here by design — the message models/serializers aren't shared source yet (only the zero-dependency ObjectFieldIds.cs + Constants.cs are).

Tests

• Unit (ProtocolTests): DisplayMessage round-trip (with and without null optional fields), serializer-id stability (id 12), protocol-version string. Mirrored in the standalone DotnetTestProtocolContract.UnitTests.
• Unit (DotnetTestPassthroughOutputDeviceTests): warning/error look up the connection; informational text is swallowed without touching the service provider.
• Acceptance (DotnetTestPipeDisplayMessageForwardingTests): at 1.3.0 a framework's warning + error are forwarded as DisplayMessage with the correct severity levels and instance-id correlation; at 1.2.0 nothing is forwarded.
• Black-box wire reader (DotnetTestPipeProtocol) extended with DisplayMessage decoding; baseline test updated to the new advertised version string.

All green locally: platform builds clean, 26 platform unit tests + 6 contract tests + 2 new acceptance tests pass, and the 7 existing AzDO-forwarding + baseline acceptance tests still pass (no regression).

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Pull request overview

This PR extends the dotnet test pipe protocol in Microsoft.Testing.Platform (MTP) to forward generic host warning/error diagnostics (not just test results or Azure DevOps logging commands) across multi-assembly runs, by introducing a new DisplayMessage wire frame and negotiating it via protocol 1.3.0.

Changes:

• Add DisplayMessage model/levels + serializer (serializer id 12) and bump ProtocolConstants.SupportedVersions to include 1.3.0.
• Update the pipe connection + output device plumbing so Warning/Error output device messages are forwarded over the protocol when the negotiated version is >= 1.3.0.
• Add/extend unit + acceptance tests, and extend the black-box acceptance wire decoder to recognize DisplayMessage.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Platform.UnitTests/OutputDevice/DotnetTestPassthroughOutputDeviceTests.cs	Adds unit coverage for warning/error forwarding lookup vs informational suppression behavior.
test/UnitTests/Microsoft.Testing.Platform.UnitTests/IPC/ProtocolTests.cs	Adds DisplayMessage round-trip tests, serializer-id stability check (id 12), and version string update.
test/UnitTests/Microsoft.Testing.Platform.DotnetTestProtocolContract.UnitTests/DotnetTestProtocolContractTests.cs	Mirrors serializer-id stability + protocol version bump in the contract test project.
test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/DotnetTestPipe/DotnetTestPipeProtocol.cs	Extends acceptance wire reader with serializer id 12 + DisplayMessage body decoding.
test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/DotnetTestPipe/DotnetTestPipeDisplayMessageForwardingTests.cs	New acceptance tests validating forwarding at 1.3.0 and absence at 1.2.0.
test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/DotnetTestPipe/DotnetTestPipeBaselineTests.cs	Updates baseline advertised-protocol expectations to include 1.3.0.
src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/IPC/Serializers/DisplayMessageSerializer.cs	New serializer for DisplayMessage (id 12) using the shared field ids/levels.
src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/IPC/ObjectFieldIds.cs	Adds embedded DisplayMessageFieldsId with stable serializer + field ids.
src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/IPC/Models/DisplayMessage.cs	New IPC model representing forwarded host diagnostics with severity.
src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/IPC/Constants.cs	Adds embedded DisplayMessageLevels + bumps supported protocol versions to 1.3.0.
src/Platform/Microsoft.Testing.Platform/ServerMode/DotnetTest/DotnetTestConnection.cs	Adds negotiation flag IsDisplayMessageForwardingSupported and sends DisplayMessage requests.
src/Platform/Microsoft.Testing.Platform/OutputDevice/OutputDeviceManager.cs	Installs DotnetTestPassthroughOutputDevice under pipe protocol unconditionally (not just on AzDO).
src/Platform/Microsoft.Testing.Platform/OutputDevice/DotnetTestPassthroughOutputDevice.cs	Forwards warning/error messages as DisplayMessage (1.3.0+) while preserving informational suppression.
src/Platform/Microsoft.Testing.Platform/IPC/Serializers/RegisterSerializers.cs	Registers DisplayMessageSerializer so frames can be sent/received under the pipe protocol.

Review details

• Files reviewed: 14/14 changed files
• Comments generated: 2
• Review effort level: Low

[Evangelink]

/azp run microsoft.testfx

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Azure Pipelines successfully started running 1 pipeline(s).

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Review details

• Files reviewed: 14/14 changed files
• Comments generated: 1
• Review effort level: Low

[Evangelink]

🧪 Test quality grade — PR #9521

12 tests graded across 5 files (7 new, 5 modified). 10 grade A, 2 grade B. Both B-grade tests are SerializerIds_AreStable in two sibling projects — their bodies slightly exceed the 30-line threshold because of the 12 serializer IDs being pinned, which is inherent to the contract-test pattern and carries no functional risk. All other tests are well-structured with meaningful assertions and descriptive names.

Δ	Test	Grade	Band	Notes
mod	DotnetTestProtocolContractTests. SerializerIds_ AreStable	B	80–89	Body just exceeds 30 lines (12 serializer pin entries + assertions); inherent to the contract-test pattern, no functional issues.
mod	ProtocolTests. SerializerIds_ AreStable	B	80–89	Body ~36 lines including a preamble comment block and 12 serializer pins; minor length only, logic is clean.
new	DotnetTestPassthroughOutputDeviceTests. DisplayAsync_ WithErrorButNoConnection_ IsSwallowedWithoutThrowing	A	90–100	No issues found.
new	DotnetTestPassthroughOutputDeviceTests. DisplayAsync_ WithInformationalText_ IsSwallowedWithoutResolvingTheConnection	A	90–100	No issues found.
new	DotnetTestPassthroughOutputDeviceTests. DisplayAsync_ WithWarningButNoConnection_ IsSwallowedWithoutThrowing	A	90–100	No issues found.
mod	DotnetTestPipeBaselineTests. DotnetTestPipe_ TestAppAdvertisesAllSupportedVersions_ NegotiatesDownToV100WithOldSdk	A	90–100	No issues found.
new	DotnetTestPipeDisplayMessageForwardingTests. DotnetTestPipe_ WhenSdkOnlySupports120_ DoesNotForwardDisplayMessages	A	90–100	No issues found.
new	DotnetTestPipeDisplayMessageForwardingTests. DotnetTestPipe_ WhenSdkSupports130_ ForwardsWarningAndErrorAsDisplayMessages	A	90–100	No issues found.
mod	DotnetTestProtocolContractTests. ProtocolVersion_ IsStable	A	90–100	No issues found.
new	ProtocolTests. DisplayMessageSerializeDeserialize	A	90–100	No issues found.
new	ProtocolTests. DisplayMessageSerializeDeserialize_ WithNullOptionalFields	A	90–100	No issues found.
mod	ProtocolTests. ProtocolVersion_ IsStable	A	90–100	No issues found.

_{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. Posted via a maintainer's GitHub token, so it appears under their account — the account owner did not write or approve this content personally. Generated by the Grade Tests on PR (on open / sync) workflow. · 405.5 AIC · ⌖ 25.4 AIC · ⊞ 43.8K · [◷]( · ◷)