Cannot debug unit test (net48 framework, xunit3)

[jansohn]

Type: Bug

Issue Description

I'm trying to debug a unit test with a legacy net48 project in VSCode. Unfortunately I'm not able to get it to stop on breakpoints.

Steps to Reproduce

1. Clone https://github.com/jansohn/vscode-xunit3
2. Open the folder in VSCode
3. Open UnitTest1.cs, set a breakpoint and press "Debug Test"

Expected Behavior

Debugger stops at breakpoint

Actual Behavior

Test runs through without stopping

Logs

OmniSharp log

Post the output from Output-->OmniSharp log here

C# log

Post the output from Output-->C# here

Environment information

VSCode version: 1.103.2
C# Extension: 2.55.29
Using OmniSharp: true

Dotnet Information

.NET SDK: Version: 8.0.202 Commit: 25674bb2f4 Workload version: 8.0.200-manifests.4e94be9c

Runtime Environment:
OS Name: Windows
OS Version: 10.0.22631
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.202\

.NET workloads installed:
There are no installed workloads to display.

Host:
Version: 8.0.19
Architecture: x64
Commit: fce8ed90dc

.NET SDKs installed:
8.0.202 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 8.0.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 8.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 8.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download

Visual Studio Code Extensions

Extension	Author	Version	Folder Name
csdevkit	ms-dotnettools	1.41.11	ms-dotnettools.csdevkit-1.41.11-win32-x64
csharp	ms-dotnettools	2.55.29	ms-dotnettools.csharp-2.55.29-win32-x64
json-tools	eriklynd	1.0.2	eriklynd.json-tools-1.0.2
powershell	ms-vscode	2025.2.0	ms-vscode.powershell-2025.2.0
prettyxml	PrateekMahendrakar	6.2.0	prateekmahendrakar.prettyxml-6.2.0
vscode-containers	ms-azuretools	2.1.0	ms-azuretools.vscode-containers-2.1.0
vscode-dotnet-runtime	ms-dotnettools	2.3.7	ms-dotnettools.vscode-dotnet-runtime-2.3.7
vscode-snippets-for-ansible	MattiasBaake	1.1.0	mattiasbaake.vscode-snippets-for-ansible-1.1.0
xml	DotJoshJohnson	2.5.1	dotjoshjohnson.xml-2.5.1

Extension version: 2.55.29
VS Code version: Code 1.103.2 (6f17636121051a53c88d3e605c491d22af2ba755, 2025-08-20T16:45:34.255Z)
OS version: Windows_NT x64 10.0.22631
Modes:

A/B Experiments

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dwcopilot:31170013
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pythonrdcb7:31342333
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[gregg-miskelly]

The recommended way to develop for .NET Framework is to use Visual Studio.

The C# extension without Dev Kit does have some very rudimentary support for debugging .NET Framework, but you will need to disable C# Dev Kit for it -- https://github.com/dotnet/vscode-csharp/blob/main/docs/debugger/Desktop-.NET-Framework.md

My understanding is that there is no way to do this with Dev Kit enabled.

[jansohn]

I don't have C# Dev Kit enabled (by setting "dotnet.preferCSharpExtension": true) as it cannot detect .NET Framework test projects anyways.

Debugging outside of unit tests also works flawlessly so I'm pretty sure this should be possible if someone with deeper knowledge were to analyze this problem.

If I disable OmniSharp ("dotnet.server.useOmnisharp": false) and run the debug test it seems to simply fail to attach the debugger correctly to the process:

.NET Test Log

Starting test discovery
Logging TestHost Diagnostics in file: c:\Users\xyz\AppData\Roaming\Code\logs\20250904T093216\window1\exthost\ms-dotnettools.csharp\testLogs\vsTestLogs.host.25-09-04_09-58-02_43546_10.txt
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v3.1.4+50e68bbb8b (64-bit .NET Framework 4.8.9310.0)
[xUnit.net 00:00:02.52]   Discovering: xunit3
[xUnit.net 00:00:02.80]   Discovered:  xunit3
Found 1 tests in 4s

Starting test run
Attaching debugger to process 17456

and in Debug Console:

------------------------------------------------------------------------------
You may only use the Microsoft Visual Studio .NET/C/C++ Debugger (vsdbg) with
Visual Studio Code, Visual Studio or Visual Studio for Mac software to help you
develop and test your applications.
------------------------------------------------------------------------------

Is this attaching the debugger step part of the C# extension or part of the xunit VSTest adapter?

[jansohn]

also according to this issue #4361 it was definitely possible at some point... Can we please re-open the issue?

[JoeRobich]

I assume it is the same issue as #8133. The C#DK extension supports the newer Microsoft Testing Platform used by xunit3. However, neither the Roslyn LSP or O# support it.

The issue seems to be that we attach the debugger to the testhost process not the test runner, now that it is a separate process.