Blocked conftest loads anyway; raises "not supposed to happen"

[osvenskan]

I'm using pytest 8.4.1, Python 3.11. I'm on a Mac, but I also see this problem in our Linux-based CI.

My test suite contains several conftest.py files in the file tree. In one context, I want to run a test suite without using a top-level conftest.py, so when I run the test suite, I do so with -p no:/Users/xxx/src/watthouse/watthouse/conftest.py.

With versions of pytest up to and including 7.4.4, this works fine. With versions ≥ 8.0.0, I get this --

AssertionError: While trying to load conftest path /Users/xxx/src/watthouse/watthouse/conftest.py, found that the module <module 'watthouse.conftest' from '/Users/xxx/src/watthouse/watthouse/conftest.py'> is already loaded with path /Users/xxx/src/watthouse/watthouse/conftest.py. This is not supposed to happen. Please report this issue to pytest.

In the debugger, I can see in consider_pluginarg() in _pytest/config/__init__.py that my -p no: option is interpreted correctly, and self.set_blocked(name) is executed. I'm not sure where to debug from there. If I can help, LMK.

This project is many years old and has accumulated a lot of pieces and parts over time, so it's far from a scenario that I can share with you so you can reproduce the problem on your end. 😕 I created a simple project with a file layout that has conftest.py in the same places, but was not able to reproduce the problem with that simple project.

pip list output

$ pip list
Package                  Version
------------------------ ------------
alembic                  1.11.2
ameff_util               1.0.66
amqp                     5.3.1
beautifulsoup4           4.12.2
billiard                 4.2.1
black                    24.4.2
blinker                  1.9.0
boto3                    1.34.65
botocore                 1.34.162
build                    1.2.2.post1
cachetools               5.5.2
celery                   5.3.4
certifi                  2025.7.14
cffi                     1.17.1
charset-normalizer       3.4.2
click                    8.2.1
click-didyoumean         0.3.1
click-plugins            1.1.1.2
click-repl               0.3.0
cryptography             44.0.2
et_xmlfile               2.0.0
factory-boy              3.3.0
Faker                    37.4.2
fastcore                 1.8.5
Flask                    2.3.3
Flask-Admin              1.6.1
Flask-Login              0.6.3
Flask-WTF                1.2.1
GeoAlchemy2              0.14.2
ghapi                    1.0.4
gitdb                    4.0.12
GitPython                3.1.44
google-api-core          2.25.1
google-api-python-client 2.106.0
google-auth              2.40.3
google-auth-httplib2     0.2.0
googleapis-common-protos 1.70.0
greenlet                 3.0.1
gunicorn                 23.0.0
httplib2                 0.22.0
idna                     3.10
iniconfig                2.1.0
itsdangerous             2.2.0
Jinja2                   3.1.6
jmespath                 1.0.1
kombu                    5.5.4
Mako                     1.3.10
MarkupSafe               3.0.2
mypy_extensions          1.1.0
openpyxl                 3.1.2
packaging                25.0
pathspec                 0.12.1
pdfminer.six             20231228
pdfplumber               0.11.0
pillow                   11.3.0
pip                      25.2
pip-tools                7.4.1
platformdirs             4.3.8
pluggy                   1.6.0
prompt_toolkit           3.0.51
proto-plus               1.26.1
protobuf                 6.31.1
psycopg2                 2.9.9
pyasn1                   0.6.1
pyasn1_modules           0.4.2
pycparser                2.22
Pygments                 2.19.2
PyJWT                    2.8.0
pyparsing                3.2.3
pypdfium2                4.30.1
pyproject_hooks          1.2.0
pytest                   8.4.1
pytest-ruff              0.4.1
python-dateutil          2.9.0.post0
pytz                     2023.3.post1
pyxlsb                   1.0.10
PyYAML                   6.0.1
redis                    5.0.1
requests                 2.32.4
rsa                      4.9.1
ruff                     0.12.3
s3transfer               0.10.4
setuptools               80.9.0
six                      1.17.0
slack-sdk                3.23.0
smmap                    5.0.2
soupsieve                2.7
SQLAlchemy               2.0.23
tenacity                 8.2.3
typing_extensions        4.14.1
tzdata                   2025.2
uritemplate              4.2.0
urllib3                  2.5.0
vine                     5.1.0
wcwidth                  0.2.13
Werkzeug                 3.0.6
wheel                    0.45.1
WTForms                  3.1.2

[The-Compiler]

Not really anything we can do without more information (as in, ideally a reproducer).

Perhaps you could help by finding the offending commit that broke things, though no guarantee that anyone will be able to fix anything only based on that either. But it'd be better than nothing at least.

To do so:

• Clone the pytest repository
• Inside your project, do a pip install -e /path/to/pytest
• Run your tests, they should fail
• In the pytest repository, do a git bisect start and git bisect bad
• Also there, do git checkout 7.4.4
• Verify that running your tests works now
• Back in the pytest repo, do git bisect good
• git will now check out the middle of the two versions
• In your project repo, run your tests
• In the pytest repo, depending on the outcome, do git bisect good or git bisect bad
• Repeat until git tells you the culprit

See Git - git-bisect Documentation.

[osvenskan]

Thanks for the clear instructions. I'll try to make time to explore this. I've developed a workaround so I'm not blocked by this issue.

Before I proceed with debugging, one question -- is it possible that what we were doing was unsupported and worked under 7.x purely by accident? I ask because the documentation says that -p is for plugins, and we were perhaps abusing its capabilities by applying it to a conftest.py file.