test(iceberg): cover partition field transform conversion

[jackylee-ch]

Changes Made

Add coverage for Iceberg partition field conversion across day, year, month, hour, and truncate transforms.

Related Issues

None.

[greptile-apps]

Greptile Summary

This PR adds a parametrized test (test_convert_partition_field_transforms) covering convert_iceberg_partition_field for YearTransform, MonthTransform, HourTransform, and TruncateTransform. The expected dtypes, transform values, and source field names are all correct.

• Year, month, and hour transforms are tested against source_id=2 (ts, a TimestampType) and expected to produce DataType.int32(), which matches the existing test_convert_iceberg_transform expectations.
• TruncateTransform(8) is tested against source_id=3 (name, a StringType) with DataType.string() as the expected output, which is also consistent with prior coverage.
• DayTransform is not folded into the new parametrized test; the pre-existing test_convert_partition_field_day never checks pf.transform, leaving that assertion gap open.

Confidence Score: 4/5

Test-only change that adds correct parametrized coverage for four partition field transforms; safe to merge.

All four parametrized cases assert the correct dtype, transform value, and source field name. The only gap is that DayTransform remains in a standalone function that never checks pf.transform, leaving that assertion untested even after this PR.

tests/io/iceberg/test_iceberg_metadata.py — the pre-existing test_convert_partition_field_day could be folded into the new parametrized test to close a missing transform assertion.

Important Files Changed

Filename	Overview
tests/io/iceberg/test_iceberg_metadata.py	Adds a parametrized test covering year, month, hour, and truncate partition field transforms; assertions look correct but DayTransform is not consolidated into the new parametrized test, leaving its transform assertion untested.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["test_convert_partition_field_transforms (parametrized)"] --> B["convert_iceberg_partition_field(SIMPLE_SCHEMA, IcebergPartitionField)"]
    B --> C{Transform}
    C --> D["YearTransform → int32, PartitionTransform.year()"]
    C --> E["MonthTransform → int32, PartitionTransform.month()"]
    C --> F["HourTransform → int32, PartitionTransform.hour()"]
    C --> G["TruncateTransform(8) → string, PartitionTransform.iceberg_truncate(8)"]
    G2["test_convert_partition_field_day (standalone)"] --> B2["convert_iceberg_partition_field"]
    B2 --> H["DayTransform → date  (transform not asserted)"]

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[greptile-apps]

DayTransform left outside the parametrized test

DayTransform is conceptually in the same family as YearTransform, MonthTransform, and HourTransform (all are time-based transforms on ts), yet it lives in the standalone test_convert_partition_field_day function. That older test also never asserts pf.transform, so the transform equality for day is currently untested. Folding the day case into test_convert_partition_field_transforms (with PartitionTransform.day() and DataType.date() as expected values) would give it the same assertion depth as the other time-based transforms and keep all similar cases in one place.

Rule Used: Prefer single parametrized functions over multiple... (source)

Learned From
Eventual-Inc/Daft#5207

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[jackylee-ch]

Updated in 9493dce: folded the DayTransform case into the parametrized transform test and added the PartitionTransform.day() assertion.