Add dotnet.config to specify MTP for dotnet test

[Youssef1313]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[Copilot]

Pull Request Overview

This PR adds a dotnet.config file to configure Microsoft.Testing.Platform (MTP) as the default test runner for dotnet test commands, eliminating the need for the -- separator in test command arguments.

• Adds dotnet.config to specify MTP as the test runner
• Updates test command syntax by removing -- separators from various configuration files
• Updates documentation to reflect the new command syntax without -- separators

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
dotnet.config	New configuration file specifying Microsoft.Testing.Platform as the test runner
tests/helix/send-to-helix-buildonhelixtests.targets	Removes -- separator from test command arguments
.github/workflows/run-tests.yml	Removes -- separator from GitHub workflow test commands
.github/copilot-instructions.md	Updates documentation examples to remove -- separators from test commands

[Youssef1313]

failed Aspire.Hosting.Testing.Tests.TestingBuilderTests.CanOverrideLaunchProfileViaArgs(launchProfileName: "http", directArgs: True) (9s 837ms)
  from /home/runner/work/aspire/aspire/artifacts/bin/Aspire.Hosting.Testing.Tests/Debug/net8.0/Aspire.Hosting.Testing.Tests (net8.0|x64)
  Assert.Equal() Failure: Strings differ
  Expected: "app-host-is-http"
  Actual:   "app-host-is-https"
                             ↑ (pos 16)
    at Aspire.Hosting.Testing.Tests.TestingBuilderTests.CanOverrideLaunchProfileViaArgs(String launchProfileName, Boolean directArgs) in /_/tests/Aspire.Hosting.Testing.Tests/TestingBuilderTests.cs:332
    at Aspire.Hosting.Testing.Tests.TestingBuilderTests.CanOverrideLaunchProfileViaArgs(String launchProfileName, Boolean directArgs) in /_/tests/Aspire.Hosting.Testing.Tests/TestingBuilderTests.cs:332

This slight change in behavior is because dotnet test considers launchSettings.json.

I see #7363 added tests/Aspire.Hosting.Testing.Tests/Properties/launchSettings.json but I'm not sure how it was supposed to work. @ReubenBond Can you please take a look?

[Youssef1313]

Adding --no-launch-profile for now to unblock this, preserving the old behavior before this PR. Let's see if this will be green now.

[Youssef1313]

@radical Assuming it's green. Can you please review so that we can get it merged?

[Youssef1313]

Ping @radical for review please.

[radical]

What does dotnet.config do exactly? Is that documented somewhere too?
Also, does it need to be added to the helix payload?

[Youssef1313]

@radical It enables the new dotnet test experience for MTP which we implemented in .NET 10 SDK. It's documented in Testing with 'dotnet test' and 'dotnet test' CLI reference.

The old way of running MTP is that MTP is hooking into the VSTest infrastructure.

Also, does it need to be added to the helix payload?

Anywhere dotnet test is run, dotnet.config is needed.