pytest discovery clobbers PYTHONPATH

[couteau]

Type: Bug

Behavior

Pytest test discovery fails, reporting a missing import. The relevant package exists and is on the PYTHONPATH in my conda environment, but the python extension resets the PYTHONPATH to /Users/username/.vscode/extensions/ms-python.python-2025.16.0-darwin-arm64/python_files when it runs test discovery (and perhaps also tests, but I can't get that far). Running from the command line works fine.

This is a new problem -- not sure exactly when it started but I was not having it in September, so maybe with the most recent version.

Steps to reproduce:

1. Create a conda environment
2. Install packages in some location other than site-packages (e.g., $CONDA_PREFIX/share/python)
3. Set the PYTHONPATH to the location of the package in the conda environement (e.g., using conda env config vars)
4. Create a project in vscode
5. Create a pytest test in the project that imports the package in the non-standard location
6. Click the refresh tests button

Diagnostic data

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

2025-10-20 12:54:38.840 [info] Running installed packages checker:  {
  id: '/Users/username/anaconda3/envs/my_conda_env/bin/python',
  displayName: 'my_conda_env (3.12.11)',
  detailedDisplayName: 'my_conda_env',
  envType: 'Conda',
  envPath: '/Users/username/anaconda3/envs/my_conda_env',
  type: 'Conda',
  path: '/Users/username/anaconda3/envs/my_conda_env/bin/python',
  version: {
    raw: '3.12.11',
    major: 3,
    minor: 12,
    patch: 11,
    build: [],
    prerelease: []
  },
  sysVersion: '3.12.11',
  architecture: 3,
  sysPrefix: '/Users/username/anaconda3/envs/my_conda_env'
} /Users/username/.vscode/extensions/ms-python.python-2025.16.0-darwin-arm64/python_files/installed_check.py /Users/username/Source/my_project/pyproject.toml
2025-10-20 12:54:38.840 [info] > ~/anaconda3/envs/my_conda_env/bin/python ~/.vscode/extensions/ms-python.python-2025.16.0-darwin-arm64/python_files/installed_check.py ./pyproject.toml
2025-10-20 12:56:03.065 [info] Discover tests for workspace name: my_project - uri: /Users/username/Source/my_project
2025-10-20 12:56:03.073 [info] arg: --rootdir already exists in args, not adding.
2025-10-20 12:56:03.073 [info] Environment variables set for pytest discovery: PYTHONPATH=/Users/username/.vscode/extensions/ms-python.python-2025.16.0-darwin-arm64/python_files, TEST_RUN_PIPE=/var/folders/7b/j6zzgg8j1v3d83xn_msb1xnw0000gn/T/python-test-discovery-59c4eedeb9119bd3c322
2025-10-20 12:56:03.253 [error] ImportError while loading conftest '/Users/username/Source/my_project/tests/conftest.py'.

2025-10-20 12:56:03.277 [error] tests/conftest.py:36: in <module>
    from qgis.core import (
E   ModuleNotFoundError: No module named 'qgis'

2025-10-20 12:56:03.297 [error] Subprocess exited unsuccessfully with exit code 4 and signal null on workspace /Users/username/Source/project_name
2025-10-20 12:56:03.297 [error] pytest test discovery error for workspace:  /Users/username/Source/project_name 
  
 The python test process was terminated before it could exit on its own, the process errored with: Code: 4, Signal: null for workspace /Users/username/Source/project_name

Extension version: 2025.16.0
VS Code version: Code 1.105.1 (7d842fb85a0275a4a8e4d7e040d2625abbf7f084, 2025-10-14T22:33:36.618Z)
OS version: Darwin arm64 24.6.0
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.10.18
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): Conda
• Value of the python.languageServer setting: Default

User Settings

condaPath: "/Users/username/anaconda3/bin/conda"

languageServer: "Pylance"

testing
• pytestArgs: ""
• pytestEnabled: true

experiments
• optInto: ["pythonTestAdapter"]

Installed Extensions

Extension Name	Extension Id	Version
cmake-tools	ms-	1.21.36
copilot	Git	1.372.0
copilot-chat	Git	0.32.3
cpptools	ms-	1.28.3
cpptools-extension-pack	ms-	1.3.1
cpptools-themes	ms-	2.0.0
datawrangler	ms-	1.22.0
debugpy	ms-	2025.14.1
even-better-toml	tam	0.21.2
hexeditor	ms-	1.11.1
intellicode-api-usage-examples	Vis	0.2.9
js-debug	ms-	1.105.0
js-debug-companion	ms-	1.1.3
js-debug-nightly	ms-	2025.10.117
jupyter	ms-	2025.9.1
jupyter-keymap	ms-	1.1.2
jupyter-renderers	ms-	1.3.0
makefile-tools	ms-	0.12.17
prettier-vscode	esb	11.0.0
python	ms-	2025.16.0
remote-containers	ms-	0.427.0
ruff	cha	2025.28.0
vscode-containers	ms-	2.2.0
vscode-js-profile-table	ms-	1.0.10
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
vscode-pylance	ms-	2025.8.3
vscode-python-envs	ms-	1.10.0
vscode-typescript-next	ms-	6.0.20251019
vscodeintellicode	Vis	1.3.2

System Info

Item	Value
CPUs	Apple M1 Max (10 x 2400)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: enabled_on trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	4, 4, 4
Memory (System)	64.00GB (0.35GB free)
Process Argv	--crash-reporter-id 7daef490-db9b-4617-abaa-559a02220920
Screen Reader	no
VM	0%

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nes-set-on:31340697
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envsactivate1:31353494
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gaj49834:31404438
cloudbuttont:31379625
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[eleanorjboyd]

Hi- to clarify when you say " python extension resets the PYTHONPATH to /Users/username/.vscode/extensions/ms-python.python-2025.16.0-darwin-arm64/python_files when it runs test discover" is that all that is left in the PYTHON PATH for you?