DEFAULT_CONFIG_FILE can cause the tox test suite to fail #3610
Description
Issue
The tox test suite does not isolate the tests from the user's system, meaning that it's possible for the test suite to load the user's DEFAULT_CONFIG_FILE if it exists.
Environment
Provide at least:
- OS: Linux
Output of pip list of the host Python, where tox is installed
$ pip list Package Version Editable project location ------------- -------------------------------- ------------------------- cachetools 6.2.0 chardet 5.2.0 colorama 0.4.6 distlib 0.4.0 filelock 3.19.1 packaging 25.0 pip 25.2 platformdirs 4.4.0 pluggy 1.6.0 pyproject-api 1.9.1 setuptools 80.9.0 tox 4.30.3.dev0+g5e0784a7f.d20250917 /home/kurt/dev/pr-tox virtualenv 20.34.0 wheel 0.45.1Output of running tox
Output of tox -rvv
FAILED ... FAILED tests/config/loader/test_loader.py::test_override_incorrect[-x] - assert not "ROOT: failed to read config file None because File contains no section headers.\nfile: '/home/kurt/.config/tox/config.ini', line: 1\n'[tox\\n'\n" FAILED ...Minimal example
$ echo '[tox' > ~/.config/tox/config.ini $ tox