TEST: Remove deterministic reshape skips

[vyasr]

Description

Prefilter reshape matrices to the combinations that previously reached assertions: melt retains every supported dtype/null pair, and pandas-comparison merge tests retain every pandas-supported join mode and categorical compatibility pair. The dedicated mixed int/float merge expectation is removed because existing type-casting merge coverage exercises that behavior. Cross joins are explicitly exercised for disjoint-column and empty-input cases, while non-cross modes retain their expected errors.

The two public copy-view node IDs are removed from the pandas expected-failure configuration because they now pass. This exposes a future regression instead of allowing either a failure or an XPASS.

Checklist

• I am familiar with the CONTRIBUTING.md guidelines.
• New or existing tests cover these test-only changes.
• Documentation updates are not needed.

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📝 Summary

Summary by CodeRabbit

• Tests
  • Expanded reshape test coverage for melt operations across numeric, boolean, datetime, and timedelta data types.
  • Improved validation of null-handling behavior for supported data types.
  • Broadened merge testing across pandas-compatible modes, including cross joins.
  • Updated ordering and compatibility checks to reflect supported merge behavior.
  • Removed obsolete test cases and skip conditions for unsupported scenarios.
  • Updated test failure tracking for copy-view indexing cases.

Walkthrough

The PR expands melt tests for numeric and temporal dtypes and updates merge tests to use shared pandas-compatible mode sets, including cross joins. It removes obsolete skips and mixed-type coverage, adds explicit categorical and merge-combination cases, and removes two pandas testing plugin failure entries.

Changes

Melt coverage

Layer / File(s)	Summary
Melt dtype and null coverage python/cudf/cudf/tests/reshape/test_melt.py	The tests cover numeric, boolean, datetime, and timedelta dtypes. Floating-point cases use multiple null patterns. Other dtypes use null-free cases. The copyright range is updated.

Merge coverage

Layer / File(s)	Summary
Merge mode parameters python/cudf/cudf/tests/reshape/test_merge.py	Shared constants define pandas-compatible merge modes with and without "cross". Pair-of-triples and empty-join tests use these modes. Disjoint-column cases preserve error assertions for non-cross modes and compare cross-join results.
Merge input cases python/cudf/cudf/tests/reshape/test_merge.py	The obsolete mixed integer/float casting test is removed. Categorical coverage uses explicit cases with one categorical operand.
Merge ordering and combinations python/cudf/cudf/tests/reshape/test_merge.py	Ordering tests use standard pandas modes. Merge-combination tests include the configured modes without conditional skips.

Pandas testing plugin mapping

Layer / File(s)	Summary
Failure mapping cleanup python/cudf/cudf/pandas/scripts/pandas-testing-plugin.py	Two copy-view indexing failure entries are removed from the failure mapping.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to cb609

The change updates reshape test coverage and expected-failure mappings without any identified merge-blocking risk.

🚥 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 10 functions across 2 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.
Title check	✅ Passed	The title clearly identifies the main change: removing deterministic skips from reshape tests. It is concise and related to the changeset.
Description check	✅ Passed	The description accurately summarizes the melt and merge test updates and the removal of two pandas expected-failure entries.

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Inline comments:
In `@python/cudf/cudf/tests/reshape/test_merge.py`:
- Line 225: Update the parameterized merge test using
PANDAS_MERGE_HOWS_WITH_CROSS so disjoint column pairs with how="cross" compare
pandas and cuDF results by passing how through to both merge calls; preserve the
existing default/error assertion behavior for other how values.

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• python/cudf/cudf/tests/reshape/test_melt.py
• python/cudf/cudf/tests/reshape/test_merge.py

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[vyasr]

/ok to test

[vyasr]

/ok to test