Convert conftest-patch.py to a pytest plugin for pandas testing

[mroeschke]

Description

This PR converts and renames conftest-patch.py to apandas-testing-plugin.py pytest plugin file that can be used as pytest -p pandas-testing-plugin to patch pandas testing utilities and dynamically add our xfail or skip markers instead of modifying the existing pandas' conftest.py.

Hoping to reduce the modifications we make to the cloned repo in a follow up PR

Additionally moves some flags set in CI scripts to the script run locally for better CI/local alignment

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[mroeschke]

/ok to test 429b4ad

[mroeschke]

/ok to test a549ef8

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Tests

  • Improved Pandas test infrastructure with restructured test plugin and assertion handling.
  • Updated test invocation to register custom testing plugins for enhanced compatibility checks.

• Chores

  • Updated linting configuration to remove redundant ignore patterns.
  • Reorganized test script imports and dependencies for better maintainability.

Walkthrough

This PR refactors pandas test warning suppression by moving helper logic from the pytest plugin into a wrapper module, updating the plugin to properly register as a pytest hook, and configuring test runners to load the new plugin directly instead of patching conftest files.

Changes

Pandas Test Warning Suppression

Layer / File(s)	Summary
Warning suppression helpers in wrapper module python/cudf/cudf/pandas/_wrappers/pandas.py	Adds contextlib import and defines null_assert_produces_warning and null_raises_chained_assignment_error context managers that redirect pandas testing assertions to suppress warnings and chained-assignment errors.
Plugin refactoring and hook registration python/cudf/cudf/pandas/scripts/pandas-testing-plugin.py	Removes the old null_assert_warnings context manager from the plugin, cleans up unused imports (contextlib, os), adds explicit @pytest.hookimpl(trylast=True) decorator to pytest_collection_modifyitems, and removes sys.path.append statement.
Test runner and configuration updates python/cudf/cudf/pandas/scripts/run-pandas-tests.sh, ci/cudf_pandas_scripts/pandas-tests/run.sh, pyproject.toml	Registers the pytest plugin via -p cudf.pandas.scripts.pandas-testing-plugin, removes the conftest patching approach, expands marker filters to exclude network tests, removes stale comment guidance, and deletes the Ruff F821 ignore for conftest-patch.py.

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

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Suggested reviewers

• pentschev
• TomAugspurger

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately describes the main change: converting conftest-patch.py to a pytest plugin for pandas testing, which aligns with the substantial refactoring in the changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining the conversion of conftest-patch.py to a pytest plugin and the movement of CI flags, matching the actual code changes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@python/cudf/cudf/pandas/_wrappers/pandas.py`:
- Around line 1512-1536: Add unit tests and a benchmark for the new proxy helper
functions: null_assert_produces_warning, _register_assert_produces_warning,
null_raises_chained_assignment_error, and
_register_raises_chained_assignment_error. Create pytest cases that verify each
helper returns a contextmanager, that using the context manager
suppresses/handles pandas warnings and chained-assignment errors as intended
(exercise both direct calls to null_* helpers and the registered proxy wrappers
_register_*), and assert proper enter/exit behavior; also add a lightweight perf
benchmark (pytest-benchmark or project benchmark style) that measures
entering/exiting these context managers to satisfy repo policy. Ensure tests
live under the repo's test pattern and include necessary imports/mocks for
pd._testing so the proxy registration is exercised.
- Around line 1512-1520: The current null_assert_produces_warning context
manager yields an empty list and doesn't capture warnings, so under
filterwarnings("error")/ -Werror warnings still raise; modify
null_assert_produces_warning to use warnings.catch_warnings(record=True) and set
a permissive filter (e.g., warnings.simplefilter("always") or "default") inside
the context so warnings are recorded rather than turned into errors, then yield
the recorded list and restore warning state on exit; update the function
null_assert_produces_warning to import and use the warnings module and return
the captured warnings list similarly to pandas.assert_produces_warning.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 3cfe15b and a549ef8.

📒 Files selected for processing (5)

• ci/cudf_pandas_scripts/pandas-tests/run.sh
• pyproject.toml
• python/cudf/cudf/pandas/_wrappers/pandas.py
• python/cudf/cudf/pandas/scripts/pandas-testing-plugin.py
• python/cudf/cudf/pandas/scripts/run-pandas-tests.sh

💤 Files with no reviewable changes (2)

• ci/cudf_pandas_scripts/pandas-tests/run.sh
• pyproject.toml

[bdice]

What does this comment mean?

[mroeschke]

I suppose I was trying to convey "this is a proxy that doesn't faithfully fall back to pandas because we need it to be a no-op when we run pandas tests". I can tune this comment in a follow up PR or a next commit if needed.

[mroeschke]

/merge