chains_test's fstat fake breaks pytest 9.2.0's capture, turning deps-latest red #713

tests/chains_test.py::test_a_descriptor_that_cannot_be_inspected_is_closed_and_refused fails under pytest 9.2.0 with OSError: no fstat, raised by the test's own fake. The test replaces os.fstat for the whole process. pytest 9.2.0's fd-level capture now calls os.fstat on its own buffer after the call phase (pytest-dev/pytest#14687), before the monkeypatch is undone, and gets the fake. cookie_auth itself behaves: the pytest.raises and the descriptor count both pass first.

The fix is in the test: the fake fails only for the cookie file's descriptor and hands every other descriptor to the real os.fstat.

What happens

deps-latest is red on main (b6491d8): https://github.com/btclib-org/bitcoin-core-rpc/actions/runs/40672783964, scheduled 2026-10-28. The four ubuntu and macos suite cells fail on this one test; windows skips it (no /dev/fd). The run's upgrade moved pytest from 9.1.1 (the lock) to 9.2.0. Expected: the suite passes at latest, as it does at the lock.

How to reproduce it

# on origin/main, at the lock: 1 passed
#   uv run pytest --no-cov -n 0 "tests/chains_test.py::test_a_descriptor_that_cannot_be_inspected_is_closed_and_refused"
# after `uv lock --upgrade` (pytest 9.2.0): 1 failed, --tb=native shows
#   _pytest/capture.py, line 595, in snap
#     if os.fstat(self.tmpfile.fileno()).st_size == 0:
#   tests/chains_test.py, line 331, in failing_fstat
#     raise OSError("no fstat")

Version

main at b6491d8

Bitcoin Core version

none: a test-suite failure, no node involved

Platform and interpreter

CPython 3.11 and 3.15, ubuntu-latest and macos-latest (CI); CPython 3.11.15, macOS arm64 (local)