[BUG] Unable to Connect to Testing Platform on Linux

[ethangillengg]

Describe the Issue

I was trying out the new Microsoft.Testing.Platform, but was getting the following error in my the C# Dev Kit - Test Explorer output in VS Code:

Created Test Controller
Log verbosity: minimal
platform: linux arch: x64
Using vstest from dotnet sdk in [/nix/store/shf7sm84b755wi2igsg4px830rglx324-dotnet-sdk-9.0.101/share/dotnet/sdk/9.0.101].
Initialized Test Explorer Server [457050]
Test Store Folder: /home/ethan/.config/Code/User/workspaceStorage/ec00d5dd03443181ee1913bf602dd53c/ms-dotnettools.csdevkit
Test data store opened in 0.028 sec.
Initialized project system provider.
1 projects added, 0 changed, 0 removed.
Scheduling discovery: /home/ethan/Code/Lab/xUnitExperiment/bin/Debug/net9.0/xUnitExperiment.dll [1734252281828]
========== Starting test discovery ==========
Unable to connect to testing platform runner process '/home/ethan/Code/Lab/xUnitExperiment/bin/Debug/net9.0/xUnitExperiment.dll'.
========== Test discovery aborted: 0 Tests found in 65.4 ms ==========
0 tests discovered from  in 65.355 ms

I found this originally when trying to use TUnit, following the exact installation instructions and example outlined in TUnit's documentation, but this issue also persisted with xUnit following the xUnit documentation.

I am also running NixOS so this may be specific to my platform.

Steps To Reproduce

1. Ensure all configuration for the extension is set to default, except:

  "dotnet.testWindow.useTestingPlatformProtocol": true

2. Create a new xunit project with dotnet new xunit3
3. Reload the VS Code window
4. Look at Output for C# Dev Kit - Test Explorer
5. See the error above
6. Also note how no tests are discovered, and running all tests does not run anything

Expected Behavior

The extension should connect to the testing platform without fail, and be able to discover tests as well as run them.

Environment Information

• OS: Linux - NixOS 25.05 (Warbler)
• VS Code Version: 1.95.3
• Extension Version: v1.15.13 (pre-release)
• Dotnet SDK Version: 9.0.101 (also tested on dotnet 8)

[ocallesp]

@fhnaseer could someone from the Test Platform take a look ?

[hh10k]

I have the same issue in a dev container on macOS with host-mode networking enabled.

Test Explorer does not work, due to the way vstest communicates between client and server. I assume this is still a problem even with useTestingPlatformProtocol?