Error collecting tests on 9.1.1 - fixtures not found when a parent directory appears multiple times in a argument list  #14635

Description

In pytest 9.1 (both 9.1.0 and 9.1.1), the computed fixture closure of a test can change depending on which unrelated paths were collected before it. When a test relies on implicit indirect parametrization — @pytest.mark.parametrize("some_fixture", [...]) where the test depends on some_fixture only transitively, not as a direct argument — collecting certain unrelated directories first causes that fixture to drop out of the closure, and collection fails with:

function uses no argument 'some_fixture'

The same test collects fine when run on its own, or when the other paths are collected in a different order. This passes on 9.0.3 and fails on 9.1.x, so it's a regression. I believe it is related to the fixture override-precedence rework (#14513 / PR #14566), which changed override ordering from registration-order to visibility/scope-order.

A test's fixture closure should be independent of what unrelated paths were collected earlier in the session.

Reproduction

This reproduces against the public Home Assistant repo (the fixture graph that triggers it is non-trivial; I have not yet reduced it to a standalone conftest.py, but the repro below is fully deterministic and takes three commands):

git clone https://github.com/home-assistant/core hass-core
cd hass-core
git checkout 957c24fcd724          # any recent dev commit works
python -m venv venv && . venv/bin/activate
pip install -r requirements_test.txt -r requirements.txt   # or: pip install -e . pytest-aiohttp syrupy ...
pip install pytest==9.1.1

# Order matters. This fails:
pytest --collect-only \
  tests/components/water_heater \
  tests/test_config_entries.py \
  tests/components/tts/test_init.py

Actual (9.1.1):

ERROR collecting tests/components/tts/test_init.py
In tests/components/tts/test_init.py::test_setup_component_no_access_cache_folder: function uses no argument 'init_tts_cache_dir_side_effect'
!!! Interrupted: 1 error during collection !!!

Expected (and actual on 9.0.3): clean collection, ~3.6k tests collected, no error.

Notes on determinism:

• Deterministic across PYTHONHASHSEED (fails on random seeds and on fixed seeds 0–5).
• The failing file passes in isolation: pytest --collect-only tests/components/tts/test_init.py ✅.
• Reversing the order (e.g. collecting tts first) also passes — it is purely the order in which the earlier paths are collected.
• --collect-only is enough; no xdist required (we originally hit it under -n auto --dist=loadfile, but it's not xdist-specific).

Why the test is structured this way (for context)

tests/components/tts/test_init.py::test_setup_component_no_access_cache_folder:

@pytest.mark.parametrize("init_tts_cache_dir_side_effect", [OSError(2, "No access")])
@pytest.mark.parametrize("setup", ["mock_setup", "mock_config_entry_setup"], indirect=True)
async def test_setup_component_no_access_cache_folder(
    hass, mock_tts_init_cache_dir, setup
):
    ...

The closure that makes the init_tts_cache_dir_side_effect parametrize valid:

• the test directly requests mock_tts_init_cache_dir (in tests/components/conftest.py)
• mock_tts_init_cache_dir → requests init_tts_cache_dir_side_effect (also tests/components/conftest.py)
• additionally, tests/components/tts/conftest.py has an autouse fixture that overrides a parent fixture and requests the same-named super:

  @pytest.fixture(autouse=True, name="mock_tts_cache_dir")
  def mock_tts_cache_dir_fixture_autouse(mock_tts_cache_dir):  # requests the parent of the same name
      return mock_tts_cache_dir

  whose parent (tests/components/conftest.py) transitively also reaches init_tts_cache_dir_side_effect.

Under 9.1 with a triggering prefix, init_tts_cache_dir_side_effect is no longer present in the closure, even though mock_tts_init_cache_dir is still requested directly — which is what makes this look like a closure-computation bug tied to the new override ordering rather than intended behavior.

Environment

• pytest 9.1.1 (also reproduces on 9.1.0); last known good: 9.0.3
• pluggy 1.6.0
• Python 3.14.5
• macOS (Darwin arm64); also seen on Linux CI (Python 3.14.5)

Suspected cause

#14513 / PR #14566 — fixture override ordering changed from registration-order to visibility-order. The order-dependence of the closure is the smell: with the new ordering, resolving an overridden fixture for the tts test appears to pick a fixturedef that no longer carries the init_tts_cache_dir_side_effect dependency, depending on what was registered while collecting earlier paths.

Related

• pytest 9.1.0 does not allow overriding fixture's parameters via @pytest.mark.parametrize(..., indirect=True) anymore #14591 — separate 9.1.0 regression ("duplicate parametrization of ''" when a fixture has params= and a test re-parametrizes it with indirect=True), fixed in 9.1.1. This report is a different problem that 9.1.1 does not fix.