test: cover str.to_time custom formats, schema and invalid raises

[jonasdedden]

Description

Non-default formats ("12-34" with "%H-%M", "01:30 PM" with "%I:%M %p"), including a lazy collect_schema() == Time assertion (the plugin had no Time mapping, which the old tests never caught), plus unparseable inputs raising a generic Exception (backends without Time support also raise, so no xfail is needed there).

Follow-up adds the series variants of the custom-format cases with nulls preserved.

What type of PR is this? (check all applicable)

• 💾 Refactor
• ✨ Feature
• 🐛 Bug Fix
• 🔧 Optimization
• 📝 Documentation
• ✅ Test
• 🐳 Other

Related issues

None. Test-only follow-up from narwhals-daft differential testing.

AI assistance

• No AI tools were used for this PR.
• AI tools were used.

Checklist

• Code follows style guide (ruff)

• Tests added

• Documented the changes (N/A, test-only, no behavior change)

• If this is your first PR to narwhals, attach a screenshot of pytest passing locally (not CI):

  PYTEST_ADDOPTS="--numprocesses=logical" \
  make run-ci DEPS="--extra pandas --extra dask --group core-tests --group sklearn --group plugins" \
  CMD="pytest tests --cov=src --cov=tests --runslow --constructors=pandas,pandas[nullable],pandas[pyarrow],pyarrow,polars[eager],polars[lazy],duckdb,sqlframe"

Note: the full-suite command above was not run. Targeted run on the CI constructor set instead: pytest tests/expr_and_series/str/to_time_test.py --constructors=pandas,pandas[nullable],pandas[pyarrow],pyarrow,polars[eager],polars[lazy],duckdb,sqlframe gives 66 passed, 5 xfailed. Also green with --constructors=ibis and --constructors=dask.

Summary by CodeRabbit

• Tests
  • Expanded coverage for custom-format time parsing with scalar values and eager series, including dash-separated hours and minutes, 12-hour AM/PM input, and null preservation.
  • Added checks for parsed values and time data types, plus invalid formats and out-of-range hours.
  • Included platform and backend-specific handling for configurations where these parsing cases are unsupported.

[jonasdedden]

Huh, this uncovered a bug already raised upstream: apache/arrow#31971 EDIT: And it's open for only 4 years now... 😓 (pyarrow things :( )
Set to xfail in 59052e2

[FBruzzesi]

Hey @jonasdedden - while reviewing I spotted an issue in polars, reported in pola-rs/polars#29247 . Also relevant for #3913 . I will wait for them to come back with a feedback before finalizing the review 🙏🏼

[FBruzzesi]

@jonasdedden FYI I just closed pola-rs/polars#29247 as those cases are now (v2.0.0) consistently resulting in a polars.exceptions.ComputeError for both engines

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between e07d56b and 152ead3.

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📒 Files selected for processing (1)

• tests/expr_and_series/str/to_time_test.py

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📝 Walkthrough

Walkthrough

The change adds tests for custom-format string-to-time parsing and invalid inputs. The tests check parsed values and null handling. Some cases include backend-specific skips or expected failures.

Changes

String-to-time parsing tests

Layer / File(s)	Summary
Custom formats and invalid inputs tests/expr_and_series/str/to_time_test.py	Adds parameterized tests for dash-separated and AM/PM time formats, each with a null value. The tests check result schemas and values. Additional cases expect errors for mismatched formats and invalid time values, with backend-specific skips and an expected failure on Windows for the AM/PM pyarrow_table case.

Priority: ⬇️ Low

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

Change: Other

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Merge Risk: ⚪ Minimal · up to 152ea

The added parsing tests are ready to merge after normal checks.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		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 3 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly identifies the test coverage added for str.to_time custom formats, schema validation, and invalid-input errors.
Description check		The description follows the repository template, identifies the test scope, marks the PR as test-only, records AI assistance, reports targeted test results, and explains that the full suite was not ru…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at @tests/expr_and_series/str/to_time_test.py:
- Line 206: Update the invalid-input test at the `pytest.raises` assertion to
exclude Dask and PySpark via the existing `requires_time_support` mechanism, so
unsupported `Time` operation errors cannot satisfy the test. On supported
backends, assert the specific parsing error expected for invalid input rather
than catching any exception.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 0806cf0b-c9b2-4fa0-8d66-fb7a70bc44f6

📥 Commits

Reviewing files that changed from the base of the PR and between 4d6f7b0 and 27b979e.

📒 Files selected for processing (1)

• tests/expr_and_series/str/to_time_test.py

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 3 remain after this review.

[FBruzzesi]

Thanks @jonasdedden 🙌🏼