Debugging pytest tests causes premature exit upon process.join()

[SebMoore]

Behaviour

Debugging any pytest test that contains code that creates a child process via multiprocessing's mp.Process() and then later waits for that process to terminate via process.join() results in the debugger exiting early.

Specifically, the debugger terminates immediately after the child process terminates. It seems as though the debugger thinks the primary process has terminated, when in fact it's a child process.

Debugging the exact same code but as a standalone python file (i.e. not a test) doesn't cause this issue.

Steps to reproduce:

1. Create a pytest file: (e.g. test_debugger.py)

import multiprocessing as mp
import time
def _child_main() -> None:
    time.sleep(0.25)

def test_multiprocessing_join_in_test_body() -> None:
    proc = mp.Process(
        target=_child_main,
        name="debug_multiprocessing_test_body_child",
    )
    proc.daemon = True
    proc.start()
    print("before!")
    proc.join(10)
    print("after!")
    assert proc.exitcode == 0

2. Open the "Testing" tab on the Activity Bar
3. Find the test and select "Debug Test"
4. The test will exit right after proc.join(10) and be marked as skipped - i.e. it will not print "after!" and will not reach the assert

Diagnostic data

launch.json configuration

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Debug Current File (.venv)",
            "type": "debugpy",
            "request": "launch",
            "program": "${file}",
            "cwd": "${workspaceFolder}",
            "python": "${workspaceFolder}\\.venv\\Scripts\\python.exe",
            "purpose": ["debug-test"],
            "console": "integratedTerminal",
            "justMyCode": false,
            "debugAdapterPath": "${workspaceFolder}\\.venv\\Lib\\site-packages\\debugpy\\adapter",
        }
    ]
}

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

2026-03-18 13:29:51.064 [info] arg: --rootdir already exists in args, not adding.
2026-03-18 13:29:51.064 [info] Attempting to use temp directory for test ids file, file name: test-ids-00c8f18e91ac982d37c4.txt
2026-03-18 13:29:51.066 [info] Environment variables set for pytest execution: PYTHONPATH=c:\Users\Seb\.vscode\extensions\ms-python.python-2026.4.0-win32-x64\python_files, TEST_RUN_PIPE=\\.\pipe\python-test-results-39db76ade74d9d04d426, RUN_TEST_IDS_PIPE=C:\Users\SEBAST~1\AppData\Local\Temp\test-ids-00c8f18e91ac982d37c4.txt
2026-03-18 13:29:51.066 [info] Running DEBUG pytest with arguments: --rootdir=c:\Users\Seb\Documents\_Repos\test_debug,--capture=no for workspace c:\Users\Seb\Documents\_Repos\test_debug 

2026-03-18 13:29:51.067 [info] Using configuration in launch.json
2026-03-18 13:29:59.546 [info] Test Result named pipe \\.\pipe\python-test-results-39db76ade74d9d04d426  cancelled

Output for Python Debugger in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python Debugger)

2026-03-18 13:29:51.452 [info] legacyGetInterpreterDetails: executable='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe' resource='c:\Users\Seb\Documents\_Repos\test_debug'
2026-03-18 13:29:51.452 [info] resolveAndUpdatePythonPath - Initial state: pythonPath='undefined', python='c:\Users\Seb\Documents\_Repos\test_debug\.venv\Scripts\python.exe', debugAdapterPython='C:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe', debugLauncherPython='C:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe', workspaceFolder='c:\Users\Seb\Documents\_Repos\test_debug'resolvedInterpreterPath='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe'
2026-03-18 13:29:51.487 [info] Resolving launch configuration with substituted variables
2026-03-18 13:29:51.503 [info] createDebugAdapterDescriptor: request='launch' name='Python: Debug Current File (.venv)'
2026-03-18 13:29:51.504 [info] legacyResolveEnvironment: Resolving environment 'C:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe'
2026-03-18 13:29:51.504 [info] legacyResolveEnvironment: Resolved executable='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe'
2026-03-18 13:29:51.504 [info] resolveEnvironment: legacy resolved executable='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe' version='3.14.2'
2026-03-18 13:29:51.504 [info] getExecutableCommand: executable='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe' version='3.14.2'
2026-03-18 13:29:51.505 [info] createDebugAdapterDescriptor: python command parts='c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe'
2026-03-18 13:29:51.505 [info] DAP Server launched with command: c:\Users\Seb\.pyenv\pyenv-win\versions\3.14.2\python.exe C:\Users\Seb\Documents\_Repos\test_debug\.venv\Lib\site-packages\debugpy\adapter
2026-03-18 13:29:52.180 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:52.184 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:52.186 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:54.283 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:58.802 [info] Resolving attach configuration with substituted variables
2026-03-18 13:29:58.802 [info] Using the only workspaceFolder found:  c:\Users\Seb\Documents\_Repos\test_debug
2026-03-18 13:29:58.808 [info] createDebugAdapterDescriptor: request='attach' name='Subprocess 34584'
2026-03-18 13:29:58.808 [info] Connecting to DAP Server at:  127.0.0.1:63314
2026-03-18 13:29:58.814 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:59.571 [info] Received 'debugpySockets' event from debugpy.
2026-03-18 13:29:59.596 [info] Received 'debugpySockets' event from debugpy.

debugpy.pydevd.34568.log
debugpy.adapter-19128.log
debugpy.pydevd.31448.log
debugpy.launcher-23484.log
debugpy.server-34568.log
debugger.vscode_5969cc3c-fa33-4f22-b0cd-4285a0e2cfe7.log
debugger.vscode_d64cf1b2-b9f0-47bf-9e42-418f78572c05.log

[SebMoore]

Not sure if this is an issue with vscode-python-debugger, vscode-python or even vscode-extension-test-runner, but putting it here for now :)

[rchiodo]

For me it just hangs. Not sure why yet.

[rchiodo]

Adding this to my launch.json lets me debug the test file as a workaround.

{
    "name": "Debug pytest multiproc",
    "type": "debugpy",
    "request": "launch",
    "module": "pytest",
    "args": ["-s", "${workspaceFolder}/tests/test_multiproc.py"],
    "console": "integratedTerminal",
}

I get the following output with your test now:

(base) (.venv312) PS C:\Users\rchiodo\source\repos\pylance-release\testing\single>  c:; cd 'c:\Users\rchiodo\source\repos\pylance-release\testing\single'; & 'c:\Users\rchiodo\source\repos\pylance-release\testing\single\.venv312\Scripts\python.exe' 'c:\Users\rchiodo\.vscode-insiders\extensions\ms-python.debugpy-2025.19.2026030601-win32-x64\bundled\libs\debugpy\launcher' '54437' '--' '-m' 'pytest' '-s' 'C:\Users\rchiodo\source\repos\pylance-release\testing\single/tests/test_multiproc.py' 
=================================================================== test session starts ===================================================================
platform win32 -- Python 3.12.10, pytest-9.0.2, pluggy-1.6.0
rootdir: C:\Users\rchiodo\source\repos\pylance-release\testing\single
collected 1 item                                                                                                                                           

tests\test_multiproc.py before!
after!
.

==================================================================== 1 passed in 2.54s ====================================================================