Test failure when /tmp/setup.py exists

I was debugging multiple test failures which I could reduce to a failure showing already in testing/test_warnings.py

pytest -s testing/test_warnings.py -k test_warning_recorded_hook
============ FAILURES ==================
_______________ test_warning_recorded_hook ____________________

pytester = <Pytester PosixPath('/tmp/pytest-of-s3248973/pytest-12/test_warning_recorded_hook0')>

>   ???
E   AssertionError: [('config warning', 'config', '', ('/tmp/pytest-of-s3248973/pytest-12/test_warning_recorded_hook0/conftest.py', 2, 'pytest_configure')), ('collect warning', 'collect', '', None), ('setup warning', 'runtest', 'pytest-of-s3248973/pytest-12/test_warning_recorded_hook0/test_warning_recorded_hook.py::test_func', None), ('call warning', 'runtest', 'pytest-of-s3248973/pytest-12/test_warning_recorded_hook0/test_warning_recorded_hook.py::test_func', None), ('teardown warning', 'runtest', 'pytest-of-s3248973/pytest-12/test_warning_recorded_hook0/test_warning_recorded_hook.py::test_func', None)]
E   assert 'pytest-of-s3...py::test_func' == 'test_warning...py::test_func'
E     - test_warning_recorded_hook.py::test_func
E     + pytest-of-s3248973/pytest-12/test_warning_recorded_hook0/test_warning_recorded_hook.py::test_func

I.e. for the recording of the warning location it uses the path under /tmp instead of only the filename.

Tracing further the outmost Collector has a nodeid of pytest-of-s3248973/pytest-12/test_warning_recorded_hook0 instead of test_warning_recorded_hook.py because session.config.rootpath is determined as /tmp, see https://github.com/pytest-dev/pytest/blob/c97a40140b2eca3ea45fcb1645d77da8cae3ee32/src/_pytest/nodes.py#L601

Following _pytest.config._initini to determine_setup to this loop https://github.com/pytest-dev/pytest/blob/c97a40140b2eca3ea45fcb1645d77da8cae3ee32/src/_pytest/config/findpaths.py#L222-L225

It starts from the test folder ancestor where the test is invoked from upwards until it finds /tmp/setup.py and then treats /tmp as the rootdir

This ultimately causes the failure.

I see 2 solutions: Ignore tempfile.gettempdir()/setup.py and/or make the tests resilient by either passing --rootdir and/or matching against path suffixes instead of full paths in the test assertions

I'm using pytest 7.2.2 w/ Python 3.9 but it should affect (almost) any version

Reproduce the failure with pytest -s testing/test_warnings.py -k test_warning_recorded_hook while /tmp/setup.py exists. Read src/_pytest/nodes.py, _pytest.config._initini, determine_setup, and the findpaths.py loop described in the issue; done means the warning location assertion no longer fails in this setup, with regression coverage or resilient assertions as appropriate.