testing: add idempotence / clean-frame-stays-clean invariant test (#164)

[naseem173]

Description

Adds tests/test_idempotence.py: a parametrized invariant test asserting that already-clean DataFrames (numeric, boolean, datetime, and text dtypes) pass through fd.clean() unchanged and record zero data-modifying actions (report.cells_changed == 0). Also includes a test reusing the existing already_clean conftest fixture, a round-trip idempotence check (fd.clean(fd.clean(df)) is a no-op), and a local sanity check confirming the invariant actually fails when a clean column is mutated, so the guard isn't vacuous.

Fixes #164

Type of Change

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Type checks (mypy) and linter checks (ruff) pass locally

Note: I wrote this against the repo's existing conventions (conftest.py, test_api.py, CONTRIBUTING.md) but could not run pytest/ruff/mypy in the environment I authored this from -- please let CI confirm before merging.

Summary by CodeRabbit

• Tests
  • Added coverage confirming cleaning already-clean data preserves values and reports no changes.
  • Verified repeated cleaning produces the same result across numeric, boolean, date/time, and text data.
  • Added safeguards ensuring meaningful text cleanup, such as trimming surrounding whitespace, remains effective.

[strix-security]

Strix is installed on this repository, but we couldn't run this PR security review because this workspace's trial has ended. Add a card to resume code reviews here.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: b796097c-ea02-474b-a074-922b856e3c59

📥 Commits

Reviewing files that changed from the base of the PR and between 4f90679 and fcebfb1.

📒 Files selected for processing (1)

• tests/test_idempotence.py

---

📝 Walkthrough

Walkthrough

Adds parametrized tests for clean numeric, boolean, datetime, and text frames, verifying that fd.clean is non-mutating, reports no changes, remains idempotent across repeated runs, and still detects surrounding whitespace mutations.

Changes

Cleaning idempotence tests

Layer / File(s)	Summary
Clean frame factories and fixture tests/test_idempotence.py	Defines already-clean DataFrame factories across multiple dtypes and exposes them through a parametrized fixture.
No-op and mutation guard assertions tests/test_idempotence.py	Checks unchanged outputs, zero reported actions, repeated-clean stability, and trimming of an intentionally mutated text value.

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

Suggested reviewers: johnnywilson-portfolio

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the added idempotence invariant test and references the linked issue.
Description check	✅ Passed	The description follows the template, summarizes the change, links the issue, and fills the change type and checklist sections.
Linked Issues check	✅ Passed	The new tests cover unchanged clean frames, zero data-modifying actions, multiple dtypes, and a mutation sanity check as required.
Out of Scope Changes check	✅ Passed	The pull request only adds the requested idempotence test module and related fixtures/tests, with no unrelated scope drift.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[kevincostner17]

Review

Looks good and ready to merge.

• Meets #164: shared clean-frame-stays-clean harness across numeric/boolean/datetime/text, plus a non-vacuous mutation sanity check.
• CI is green (quality-fast, test-matrix 3.9–3.13, TruthBench, Gauntlet).
• Local spot-check of the four factories: cells_changed == 0 and frame equality hold.

Non-blocking nits

• Prefer return_report=True over the report=True alias for consistency with docs/tests.
• not any(action.count…) is redundant with cells_changed == 0 (same underlying sum).

Approving.

[JohnnyWilson16]

Excellent work on the idempotence tests — clear, thorough, and aligned with our conventions. The round‑trip check and mutation sanity guard are especially valuable. Thanks for raising the bar on test coverage, looking forward to more of your contributions!