TEST: Focus concat input matrices

[vyasr]

Description

Replace broad DataFrame concat input Cartesian products with representative input pairs. The selected cases retain distinct DataFrame/Series/list shapes, dtypes, column names, index forms, and existing-buffer behavior.

Checklist

• I am familiar with the Contributing Guidelines.
• Existing tests cover these test-only changes.
• Documentation updates are not needed.

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[vyasr]

/ok to test

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📥 Commits

Reviewing files that changed from the base of the PR and between 34f116a and 71f4a08.

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• python/cudf/cudf/tests/reshape/test_concat.py

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📝 Summary

Summary by CodeRabbit

• Tests
  • Expanded concatenation test coverage for empty, indexed, overlapping, and repeated DataFrame combinations.
  • Consolidated reusable test scenarios while preserving existing behavior and test interfaces.
  • No user-facing functionality or production behavior changed.

Walkthrough

The concatenation tests now define reusable DataFrame and input collections at module scope. Parameterized tests reference these collections and add explicit indexed, empty, overlapping, and repeated DataFrame combinations.

Changes

Concatenation test parameterization

Layer / File(s)	Summary
List-input test collections python/cudf/cudf/tests/reshape/test_concat.py	test_dataframe_concat_lists and test_dataframe_concat_dataframe_lists use reusable collections. The cases include indexed, empty, overlapping, and repeated DataFrames.
DataFrame-input test collections python/cudf/cudf/tests/reshape/test_concat.py	test_dataframe_concat_dataframe uses reusable DataFrame and single-DataFrame collections while preserving existing input combinations.

Priority: ⬇️ Low

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

Merge Risk: ⚪ Minimal · up to 71f4a

This updates DataFrame concat test inputs to reusable representative collections without changing production behavior. No current merge-blocking risk remains.

Suggested reviewers: bdice, 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 6 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the test-only change: it narrows DataFrame concat inputs to representative pairs while preserving coverage across input types, shapes, dtypes, column names, index form…
Title check	✅ Passed	The title accurately summarizes the main change by stating that concat test input matrices are being focused. It is concise and specific enough for the changeset.
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 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[mroeschke]

Some nits: OK in a follow up

[mroeschke]

nit: Not really fond of these _DATAFRAME_* variables defined once for 1 test. When I was refactoring tests, I preferred inlining to reduce indirection as these are relatively "frozen"

[mroeschke]

Like in your other PR, these pytest.params are superfluous and below too

[vyasr]

/merge