fix #13564 - warn when fixtures get wrapped with a decorator

[RonnyPfannschmidt]

• closes Fixture definition check in parsefactories is too strict #13564

[Copilot]

Pull Request Overview

This PR adds a warning mechanism to detect when pytest fixtures are wrapped with custom decorators, which prevents pytest from discovering them during collection. The warning helps developers understand why their fixtures might not be working as expected.

Key Changes:

• Added a warning system that detects fixtures wrapped in decorators using functools.wraps
• Implemented safe wrapper chain traversal with loop detection and special object handling
• Added comprehensive test coverage for the new warning functionality

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/_pytest/fixtures.py	Implements the core detection logic for wrapped fixtures and issues warnings when found
testing/python/fixtures.py	Adds test case to verify the warning is correctly issued for decorated fixtures
changelog/13564.improvement.rst	Documents the new warning feature for wrapped fixtures

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[Zac-HD]

lgtm

[Zac-HD]

LGTM with two suggestions

[Zac-HD]

Suggested change

	seen: set[int] = set()
	for _ in range(100):
	if current is None:
	break
	current_id = id(current)
	if current_id in seen:
	return None
	seen: set[int] = {id(None)}
	for _ in range(100):
	current_id = id(current)
	if current_id in seen:
	break

[Zac-HD]

I'd prefer to make these module-level imports, at least for the stdlib which can't cause import cycles

[The-Compiler]

This seems to be mostly reimplementing Python's inspect.unwrap()?

[The-Compiler]

If I'm understanding this properly, we end up warning about this rather than making it work. Is this a reasonable course of action? Especially for the very common case of an user doing:

import pytest

class TestFixture:

    # @classmethod
    @pytest.fixture(scope="class")
    def fixt(cls):
        ...

    def test_fixt(self, fixt):
        pass

and pytest telling them to add @classmethod, I don't think this warning message will actually help them realize what's going on there.

However this also doesn't actually seem to be working with @classmethod, see my other comment.

[RonnyPfannschmidt]

no magic fixing - we have to warn/error

[The-Compiler]

Please add a test using @classmethod (#13507), I don't see any warning with:

import pytest

class TestFixture:

    @classmethod
    @pytest.fixture(scope="class")
    def fixt(cls):
        ...

    def test_fixt(self, fixt):
        pass