Illustrate failure to configure warnings in pytest

app.py

class MyDeprecationWarning(DeprecationWarning):
    pass

conftest.py

import warnings

from app import MyDeprecationWarning


def pytest_configure():
    # Configure app specific warning as error.
    warnings.filterwarnings("error", category=MyDeprecationWarning)

Dockerfile

FROM ghcr.io/astral-sh/uv:python3.13-bookworm
RUN uv python install 3.7 3.13

RUN mkdir /demo
WORKDIR /demo
ADD app.py conftest.py test_depwarn.py /demo/

RUN uv init --python 3.7 && uv add 'pytest>3,<3.1'
RUN uv run pytest

RUN uv python pin 3.13 && uv add 'pytest>7'
RUN uv run pytest

test_depwarn.py

import warnings

import pytest

from app import MyDeprecationWarning


def test_deprecated():
    with pytest.raises(MyDeprecationWarning):
        warnings.warn("Stuff deprecated", category=MyDeprecationWarning)