Generated projects fail dotnet test since xunit.v3 4.0 moved to Microsoft.Testing.Platform

[devantler]

🤖 Generated by the Agentic Engineer

Evidence

🧱 Validate Scaffold has failed on every pull request since #394 (Dependabot, 2026-08-31) bumped xunit.v3 from 3.2.2 to 4.0.0. #393, merged the same day, was the last green run. The check is not required, so twenty-odd PRs have merged over it.

The failing step renames the placeholders in a scratch copy and runs dotnet test, which stops with:

Testing with VSTest target is no longer supported by Microsoft.Testing.Platform on .NET 10 SDK and later.

Reproduced locally on SDK 10.0.302 against this repository's main:

Setup	Command	Result
as shipped	dotnet test	the error above, exit 1
global.json opts into the new test runner	dotnet test	5 of 5 tests pass, exit 0
as shipped	the shared run-dotnet-tests command (dotnet test --no-restore --collect:"XPlat Code Coverage" --logger "console;verbosity=detailed")	the same error, exit 1
global.json opts into the new test runner	the same shared command	zero tests run, exit 5

Who this affects

Anyone who creates a project from this template. Their first dotnet test fails, and the ruleset-injected test workflow from devantler-tech/actions fails too. It stays hidden here because this repository's PRs run no test job, and the shared action's own fixtures still use xunit 2.9.3 on the old runner, so its CI stays green.

Expected behaviour

A freshly generated project passes dotnet test locally and in the shared test workflow, and Validate Scaffold is green again.

Acceptance criteria

• global.json opts into Microsoft.Testing.Platform, so plain dotnet test passes in a generated project.
• devantler-tech/actions run-dotnet-tests runs tests and collects coverage under the new runner, for example through the platform's own coverage extension instead of the VSTest --collect and --logger flags, and its fixtures include an xunit.v3 4.x project so this cannot regress unseen.
• Validate Scaffold passes on a PR here, and a test job passes for a project generated from the template.
• The two changes land in an order that keeps generated projects working: the shared action first, or both together.

Rough size: S here, M in the shared action.

[devantler]

🤖 Generated by the Agentic Engineer

Delivery in progress (2026-09-15). Two pull requests, in this order:

1. fix(run-dotnet-tests): run projects opted into Microsoft.Testing.Platform actions#1264 (ships first): the shared test action now detects a project that opts into Microsoft.Testing.Platform.
   • With the code coverage extension referenced, it runs tests and collects Cobertura coverage.
   • Without it, it still runs the tests and explains that coverage was skipped.
   • Projects on the old runner are unchanged. New fixtures cover both new cases on Linux, Windows and macOS.
2. fix(tests): opt the scaffold into Microsoft.Testing.Platform #423 (after #1264 ships and the org test workflow picks it up): global.json opts into the new runner, and the test project references the coverage extension.

Local evidence (SDK 10.0.302):

Check	Result
New action step, opted-in fixture with the coverage extension	exit 0, 1 passed, 1 Cobertura report
New action step, opted-in fixture without the extension	exit 0, 1 passed, notice, no report
Old single command on an opted-in fixture	exit 5, zero tests (the failure generated projects hit today)
scripts/rename-placeholders.test.sh with this branch's opt-in	PASS end to end, including build and test
New action step on a copy of this template	exit 0, 5 passed, 1 Cobertura report