`tests/test_integration.py::test_prog` fails with Python 3.14 when starting via `python -m pytest`

[mgorny]

Summary

Python 3.14 changed the way the default prog= value is computed. When the program is run via python -m ..., it uses that value rather than argv[0]. As a result, when tests are run via python -m pytest, I'm getting the following failure:

$ python -m pytest 
========================================================= test session starts =========================================================
platform linux -- Python 3.14.0b2, pytest-8.3.5, pluggy-1.6.0
rootdir: /tmp/argh
configfile: pyproject.toml
plugins: cov-6.1.1
collected 170 items                                                                                                                   

tests/test_assembling.py ......................................                                                                 [ 22%]
tests/test_completion.py ...                                                                                                    [ 24%]
tests/test_decorators.py ......                                                                                                 [ 27%]
tests/test_dispatching.py ........                                                                                              [ 32%]
tests/test_dto.py ....                                                                                                          [ 34%]
tests/test_integration.py ...........................................F...........                                               [ 67%]
tests/test_interaction.py .....                                                                                                 [ 70%]
tests/test_mapping_policies.py ..........................                                                                       [ 85%]
tests/test_regressions.py .............                                                                                         [ 92%]
tests/test_typing_hints.py ........                                                                                             [ 97%]
tests/test_utils.py ....                                                                                                        [100%]

============================================================== FAILURES ===============================================================
______________________________________________________________ test_prog ______________________________________________________________

capsys = <_pytest.capture.CaptureFixture object at 0x7fa524b72ba0>

    def test_prog(capsys: pytest.CaptureFixture[str]):
        "Program name propagates from sys.argv[0]"
    
        def cmd(*, foo=1):
            return foo
    
        parser = DebugArghParser()
        parser.add_commands([cmd])
    
        usage = get_usage_string()
    
        assert run(parser, "-h", exit=True) == 0
        captured = capsys.readouterr()
>       assert captured.out.startswith(usage)
E       AssertionError: assert False
E        +  where False = <built-in method startswith of str object at 0x7fa524aa3cb0>('usage: __main__.py [-h] {cmd} ...\n\n')
E        +    where <built-in method startswith of str object at 0x7fa524aa3cb0> = 'usage: python -m pytest [-h] {cmd} ...\n\npositional arguments:\n  {cmd}\n    cmd\n\noptions:\n  -h, --help  show this help message and exit\n'.startswith
E        +      where 'usage: python -m pytest [-h] {cmd} ...\n\npositional arguments:\n  {cmd}\n    cmd\n\noptions:\n  -h, --help  show this help message and exit\n' = CaptureResult(out='usage: python -m pytest [-h] {cmd} ...\n\npositional arguments:\n  {cmd}\n    cmd\n\noptions:\n  -h, --help  show this help message and exit\n', err='').out

tests/test_integration.py:815: AssertionError
========================================================== warnings summary ===========================================================
tests/test_dispatching.py::test_dispatch_command_two_stage
  /tmp/argh/src/argh/dispatching.py:168: DeprecationWarning: The argument `namespace` in `dispatch()` is deprecated. It will be removed in the next minor version after v0.31.
    warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================================================= short test summary info =======================================================
FAILED tests/test_integration.py::test_prog - AssertionError: assert False
============================================== 1 failed, 169 passed, 1 warning in 0.32s ===============================================

To Reproduce

uv venv -p 3.14
uv pip install -e .[test]
.venv/bin/python -m pytest

Expected behavior

Tests passing.

Environment

• OS: Gentoo Linux amd64
• Python version: 3.14.0b2
• Argh version: 8d25286

[neithere]

As usual, thank you Michał for reporting yet another compatibility issue vs a new Python version.

The test fails on python -m pytest ≠ python -m pytest under Python 3.14 and not earlier ones.
I suspect that the reason is a recent change in argparse.ArgumentParser.add_subparsers:

Changed in version 3.14: Subparser’s prog is no longer affected by a custom usage message in the main parser.

I'll get around to it ASAP. Please feel free to contribute if you feel like it 🙂