gistfile1.txt

import pytest
import warnings
import threading


def raise_warning():
    warnings.warn(RuntimeWarning())


def test_pytest_warns():
    b = threading.Barrier(2)

    def catch_warning():
        b.wait()
        with pytest.warns(RuntimeWarning):
            raise_warning()

    task1 = threading.Thread(target=catch_warning)
    task2 = threading.Thread(target=catch_warning)

    task1.start()
    task2.start()
    task1.join()
    task2.join()

gistfile2.txt

goldbaum at Nathans-MBP in ~/Documents/test
○  pytest test.py -Werror
=============================================================== test session starts ================================================================
platform darwin -- Python 3.13.0b1, pytest-8.2.1, pluggy-1.5.0
rootdir: /Users/goldbaum/Documents/test
plugins: hypothesis-6.102.4, repeat-0.9.3
collected 1 item

test.py F                                                                                                                                    [100%]

===================================================================== FAILURES =====================================================================
________________________________________________________________ test_pytest_warns _________________________________________________________________

cls = <class '_pytest.runner.CallInfo'>, func = <function call_and_report.<locals>.<lambda> at 0x233b8964f60>, when = 'call'
reraise = (<class '_pytest.outcomes.Exit'>, <class 'KeyboardInterrupt'>)

    @classmethod
    def from_call(
        cls,
        func: Callable[[], TResult],
        when: Literal["collect", "setup", "call", "teardown"],
        reraise: Optional[
            Union[Type[BaseException], Tuple[Type[BaseException], ...]]
        ] = None,
    ) -> "CallInfo[TResult]":
        """Call func, wrapping the result in a CallInfo.

        :param func:
            The function to call. Called without arguments.
        :param when:
            The phase in which the function is called.
        :param reraise:
            Exception or exceptions that shall propagate if raised by the
            function, instead of being wrapped in the CallInfo.
        """
        excinfo = None
        start = timing.time()
        precise_start = timing.perf_counter()
        try:
>           result: Optional[TResult] = func()

../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/runner.py:341:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/runner.py:241: in <lambda>
    lambda: runtest_hook(item=item, **kwds), when=when, reraise=reraise
../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/pluggy/_hooks.py:513: in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/pluggy/_manager.py:120: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/threadexception.py:87: in pytest_runtest_call
    yield from thread_exception_runtest_hook()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    def thread_exception_runtest_hook() -> Generator[None, None, None]:
        with catch_threading_exception() as cm:
            try:
                yield
            finally:
                if cm.args:
                    thread_name = (
                        "<unknown>" if cm.args.thread is None else cm.args.thread.name
                    )
                    msg = f"Exception in thread {thread_name}\n\n"
                    msg += "".join(
                        traceback.format_exception(
                            cm.args.exc_type,
                            cm.args.exc_value,
                            cm.args.exc_traceback,
                        )
                    )
>                   warnings.warn(pytest.PytestUnhandledThreadExceptionWarning(msg))
E                   pytest.PytestUnhandledThreadExceptionWarning: Exception in thread Thread-2 (catch_warning)
E
E                   Traceback (most recent call last):
E                     File "/Users/goldbaum/Documents/test/test.py", line 16, in catch_warning
E                       raise_warning()
E                       ~~~~~~~~~~~~~^^
E                     File "/Users/goldbaum/Documents/test/test.py", line 7, in raise_warning
E                       warnings.warn(RuntimeWarning())
E                       ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
E                   RuntimeWarning
E
E                   During handling of the above exception, another exception occurred:
E
E                   Traceback (most recent call last):
E                     File "/Users/goldbaum/.pyenv/versions/3.13.0b1/lib/python3.13/threading.py", line 1039, in _bootstrap_inner
E                       self.run()
E                       ~~~~~~~~^^
E                     File "/Users/goldbaum/.pyenv/versions/3.13.0b1/lib/python3.13/threading.py", line 990, in run
E                       self._target(*self._args, **self._kwargs)
E                       ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E                     File "/Users/goldbaum/Documents/test/test.py", line 15, in catch_warning
E                       with pytest.warns(RuntimeWarning):
E                           raise_warning()
E                     File "/Users/goldbaum/.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/recwarn.py", line 318, in __exit__
E                       fail(
E                       ~~~~^
E                           f"DID NOT WARN. No warnings of type {self.expected_warning} were emitted.\n"
E                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E                           f" Emitted warnings: {found_str()}."
E                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E                       )
E                       ^
E                     File "/Users/goldbaum/.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/outcomes.py", line 177, in fail
E                       raise Failed(msg=reason, pytrace=pytrace)
E                   Failed: DID NOT WARN. No warnings of type (<class 'RuntimeWarning'>,) were emitted.
E                    Emitted warnings: [].

../../.pyenv/versions/3.13.0b1/lib/python3.13/site-packages/_pytest/threadexception.py:77: PytestUnhandledThreadExceptionWarning
============================================================= short test summary info ==============================================================
FAILED test.py::test_pytest_warns - pytest.PytestUnhandledThreadExceptionWarning: Exception in thread Thread-2 (catch_warning)
================================================================ 1 failed in 0.14s =================================================================