Avoid MSB4011 duplicate-import warnings when layering MSTest.Sdk on another base SDK

[Evangelink]

Fixes #9562.

Problem

MSTest.Sdk implicitly imports Microsoft.NET.Sdk as its base SDK in both Sdk.props and Sdk.targets. When MSTest.Sdk is layered on top of a different base SDK (for example Microsoft.NET.Sdk.Web for an ASP.NET Core integration test project) using manual SDK imports, the base Microsoft.NET.Sdk gets imported twice and the build emits MSB4011 duplicate-import warnings:

warning MSB4011: "...\Microsoft.NET.Sdk\Sdk\Sdk.props" cannot be imported again.
It was already imported at "...\Microsoft.NET.Sdk.Web\Targets\Sdk.Server.props".

Fix

Guard the Microsoft.NET.Sdk import behind a new _MSTestSdkImportsMicrosoftNETSdk property. Microsoft.NET.Sdk sets UsingMicrosoftNETSdk=true very early (before anything else), so MSTest.Sdk can detect whether an outer SDK has already imported the base SDK and skip re-importing it. The decision is recorded in Sdk.props and reused in Sdk.targets so both stay in sync — when layered, the outer SDK owns the base import.

The common <Project Sdk="MSTest.Sdk"> usage is unchanged: UsingMicrosoftNETSdk is unset at that point, so MSTest.Sdk still imports the base SDK exactly as before.

Changes

• src/Package/MSTest.Sdk/Sdk/Sdk.props.template — compute _MSTestSdkImportsMicrosoftNETSdk and gate the base props import on it.
• src/Package/MSTest.Sdk/Sdk/Sdk.targets — gate the base targets import on the same property.
• src/Package/MSTest.Sdk/README.md — document the first-class layering pattern (import the base SDK first).
• test/IntegrationTests/MSTest.Acceptance.IntegrationTests/SdkTests.cs — new acceptance test MSTestSdk_LayeredOnTopOfWebSdk_BuildsWithoutDuplicateImportWarnings that builds a Microsoft.NET.Sdk.Web + MSTest.Sdk project, asserts it runs, and asserts no MSB4011 in the output.

Verification

Reproduced the scenario with the real base SDKs plus a control:

Scenario	... cannot be imported again (MSB4011)
Mixed Web SDK, unguarded (before)	12
Mixed Web SDK, guarded (after)	0
Normal single-SDK (after)	0 — base SDK still imported, compiles cleanly

[Copilot]

Pull request overview

This PR improves MSTest.Sdk’s behavior when it’s layered on top of another SDK (e.g., Microsoft.NET.Sdk.Web) via manual Sdk.props/Sdk.targets imports by preventing duplicate imports of Microsoft.NET.Sdk that would otherwise produce MSB4011 warnings.

Changes:

• Add _MSTestSdkImportsMicrosoftNETSdk in Sdk.props to detect whether an outer SDK already imported Microsoft.NET.Sdk, and conditionally skip re-importing it.
• Use the same _MSTestSdkImportsMicrosoftNETSdk decision in Sdk.targets to keep props/targets imports in sync and avoid duplicate-import warnings.
• Add an acceptance test that builds and runs a Microsoft.NET.Sdk.Web + MSTest.Sdk manually-layered project and asserts no MSB4011 appears in build output; document the layering pattern in the SDK README.

Show a summary per file

File	Description
test/IntegrationTests/MSTest.Acceptance.IntegrationTests/SdkTests.cs	Adds an acceptance test covering the mixed/manual SDK import scenario and asserting MSB4011 is absent.
src/Package/MSTest.Sdk/Sdk/Sdk.targets	Conditionally imports Microsoft.NET.Sdk targets only when MSTest.Sdk performed the base SDK import.
src/Package/MSTest.Sdk/Sdk/Sdk.props.template	Computes _MSTestSdkImportsMicrosoftNETSdk and conditionally imports Microsoft.NET.Sdk props to prevent duplicate-import warnings.
src/Package/MSTest.Sdk/README.md	Documents the recommended manual layering pattern (base SDK first) and explains the guard behavior.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Low

[github-actions]

🧪 Test quality grade — PR #9565

Grade	Test	Notes
A (90–100)	new SdkTests. MSTestSdk_ LayeredOnTopOfWebSdk_ BuildsWithoutDuplicateImportWarnings	Well-structured acceptance test asserting MSB4011 absence and end-to-end execution of the layered project.

_{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. · 56.5 AIC · ⌖ 7.79 AIC · ⊞ 9.5K · [◷]( · ◷)