TEST: Reuse I/O test fixtures

[vyasr]

Description

Make shared I/O source data module-scoped, and construct the expensive ORC nested-list data only for the selected parameterized case.

The fixtures are read-only to surrounding tests; the two tests that mutate a pandas frame now copy it first. All original formats, assertions, and parameterized I/O cases remain executed unchanged.

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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📥 Commits

Reviewing files that changed from the base of the PR and between a8ad204 and aa12784.

📒 Files selected for processing (8)

• python/cudf/cudf/tests/input_output/test_csv.py
• python/cudf/cudf/tests/input_output/test_dlpack.py
• python/cudf/cudf/tests/input_output/test_feather.py
• python/cudf/cudf/tests/input_output/test_hdf5.py
• python/cudf/cudf/tests/input_output/test_json.py
• python/cudf/cudf/tests/input_output/test_orc.py
• python/cudf/cudf/tests/input_output/test_parquet.py
• python/cudf/cudf/tests/input_output/test_s3.py

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📝 Summary

Summary by CodeRabbit

• Tests

  • Improved input/output test efficiency by reusing shared test fixtures across modules.
  • Expanded ORC list-writer coverage for nested lists, nulls, empty elements, variable lengths, and large child collections.
  • Prevented test data mutations from affecting other cases by isolating copied inputs.
  • Added clarifying documentation for shared test data usage in DLPack and HDF5 tests.

• Documentation

  • Updated copyright attribution details in selected test files.

Walkthrough

Changes

The input/output test modules now reuse module-scoped fixtures. JSON and Parquet tests isolate mutations by copying pandas inputs. ORC list tests use named data cases and a shared builder.

Input/output test maintenance

Layer / File(s)	Summary
Module-scoped test fixtures python/cudf/cudf/tests/input_output/test_csv.py, test_dlpack.py, test_feather.py, test_hdf5.py, test_json.py, test_parquet.py, test_s3.py, test_orc.py	Fixtures use module scope. Comments document shared or read-only fixture data. SPDX notices include updated attribution where changed.
Mutable test-input isolation python/cudf/cudf/tests/input_output/test_json.py, test_parquet.py	Tests copy pandas inputs before removing columns or modifying them.
Named ORC list test cases python/cudf/cudf/tests/input_output/test_orc.py	ORC list tests use named cases and _make_orc_list_data(case) for nested, null, empty, variable-length, and large-child datasets.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to aa127

This updates test-fixture reuse and lazy ORC test-data construction without changing product behavior or stated test coverage. No merge-blocking risk remains.

Suggested reviewers: mroeschke

🚥 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 32 functions across 8 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Description check	✅ Passed	The description clearly explains fixture reuse, lazy ORC test-data construction, copy-on-mutation changes, and preserved test coverage. It directly matches the changeset.
Title check	✅ Passed	The title accurately summarizes the primary change: reusing I/O test fixtures through module scoping.

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✨ Finishing Touches 💡 1

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[bdice]

/merge