VSCode pytest test discovery fails

Question

Pytest test discovery is failing. The UI states:

Test discovery error, please check the configuration settings for the tests

The output window states:

Test Discovery failed: 
Error: Traceback (most recent call last):
  File "C:\Users\mikep\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\testing_tools\run_adapter.py", line 16, in <module>
    main(tool, cmd, subargs, toolargs)
  File "C:\Users\mikep\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\testing_tools\adapter\__main__.py", line 90, in main
    parents, result = run(toolargs, **subargs)
  File "C:\Users\mikep\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\testing_tools\adapter\pytest.py", line 43, in discover
    raise Exception('pytest discovery failed (exit code {})'.format(ec))
Exception: pytest discovery failed (exit code 3)

Here are my settings:

{
    "python.pythonPath": ".venv\\Scripts\\python.exe",
    "python.testing.pyTestArgs": [
        "tests"
    ],
    "python.testing.unittestEnabled": false,
    "python.testing.nosetestsEnabled": false,
    "python.testing.pyTestEnabled": true
}

I can run pytest from the command line successfully FWIW.

Answer 1

I spent ages trying to decipher this unhelpful error after creating a test that had import errors. Verify that your test suite can actually be executed before doing any deeper troubleshooting.

pytest --collect-only is your friend.

Answer 2

This is not a complete answer as I do not know why this is happening and may not relate to your problem, depending how you have your tests structured.

I resolved this issue by putting an __init__.py file in my tests folder

E.G.:

├───.vscode
│       settings.json
│
├───app
│       myapp.py
│
└───tests
        test_myapp.py
        __init__.py

this was working a few days ago without this but the python extension was recently updated. I am not sure if this is the intended behavior or a side effect of how discoveries are now being made

https://github.com/Microsoft/vscode-python/blob/master/CHANGELOG.md
Use Python code for discovery of tests when using pytest. (#4795)