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Incompatibility with pytest-forked #313
Description
import time
import json
import pytest
import numpy as np
def test_TMP():
np.random.seed(int(time.time()))
if np.random.rand() > 0.2:
qByUser = "1e"
json.loads(qByUser).decode("utf-8")pytest --reruns=10 --reruns-delay=1 --only-rerun=JSONDecodeError --forked test_tmp.py
============================================================================================================================= test session starts ==============================================================================================================================
platform linux -- Python 3.10.12, pytest-8.4.2, pluggy-1.6.0
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
rootdir: /mnt/home/duburcqa/workspace/src
plugins: dash-3.2.0, forked-1.6.0, print-1.2.0, random-order-1.2.0, rerunfailures-15.1, xdist-3.8.0, syrupy-5.0.0
collected 1 item
test_tmp.py F [100%]
=================================================================================================================================== FAILURES ===================================================================================================================================
___________________________________________________________________________________________________________________________________ test_TMP ___________________________________________________________________________________________________________________________________
def test_TMP():
np.random.seed(int(time.time()))
if np.random.rand() > 0.2:
qByUser = "1e"
> qUserData = json.loads(qByUser).decode("utf-8")
test_tmp.py:12:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/usr/lib/python3.10/json/__init__.py:346: in loads
return _default_decoder.decode(s)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = <json.decoder.JSONDecoder object at 0x7313fb84efe0>, s = '1e', _w = <built-in method match of re.Pattern object at 0x7313fb9075e0>
def decode(self, s, _w=WHITESPACE.match):
"""Return the Python representation of ``s`` (a ``str`` instance
containing a JSON document).
"""
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
end = _w(s, end).end()
if end != len(s):
> raise JSONDecodeError("Extra data", s, end)
E json.decoder.JSONDecodeError: Extra data: line 1 column 2 (char 1)
/usr/lib/python3.10/json/decoder.py:340: JSONDecodeError
=========================================================================================================================== short test summary info ============================================================================================================================
FAILED test_tmp.py::test_TMP
============================================================================================================================== 1 failed in 0.13s ===============================================================================================================================
Activity
The-Compiler commentedon Oct 17, 2025
This has nothing to do with either pytest-forked or pytest-rerunfailures. You're loading invalid JSON data (
1e) and getting an exception that it is, indeed, invalid json data.duburcqa commentedon Oct 17, 2025
It does... Try running this example without
--forkedand it will pass. Please read my snippet more carefully. There is a probability to just do nothing (which obviously passes). Do you think I'm taking time to report issues without testing on my side before?The-Compiler commentedon Oct 17, 2025
My bad, I was indeed wrong there. That being said, it really doesn't help to have an overly complicated example, and a traceback that does not match the code in the example.
Here's a simpler example:
It indeed fails without reruns with
pytest --reruns=10 --forked test_tmp.py, but works without--forked.janmrow commentedon Aug 26, 2026
I spent some time looking on it from current
master.The issue is not
fork()itself. The conflict happens atpytest_runtest_protocol:pytest-forkedtakes that hook first and runs one attempt, so the rerun loop inpytest-rerunfailuresis never reached. A minimal fake plugin reproduces the same behavior without forking.Simply reversing hook order is not a fix. Reruns come back, but
pytest-forkedis then bypassed and the attempts run in the parent process.I also tried a simple prototype where
pytest-rerunfailuresdelegates each attempt topytest-forked. That can make the reruns fork correctly, but it loses exception state needed by features such as--only-rerun/--rerun-except, so it creates regression.A proper fix would probably need a cleaner per-attempt API between the plugins, returning enough information for
pytest-rerunfailuresto make the rerun decision (before reports are published). That seems much larger than a small compatibility fix.LouisDeconinck commentedon Sep 17, 2026
I looked into this on current master. As the earlier investigation found, the conflict is that both plugins override
pytest_runtest_protocol: pytest-forked's implementation runs the single (forked) attempt, so rerunfailures' rerun loop is never reached. Reversing hook order either kills reruns or bypasses forking — the two plugins would need a shared per-attempt execution API for a real fix.Until that exists, I've opened a PR documenting the incompatibility in the README so users at least know reruns silently do not happen under
--forked.