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Deep dive: pandas test parity audit — fill xs test coverage gaps#261

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Deep dive: pandas test parity audit — fill xs test coverage gaps#261
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Copilot AI commented Apr 30, 2026

Audit of test parity against pandas' own test suite: are we pinning every behaviour the implementation supports? File-level coverage is complete, but assertion-level coverage is uneven — xs is the worked example.

Audit findings

  • File-level: every src/<module>/<file>.ts has a matching tests/<module>/<file>.test.ts. Sole exception: the abstract src/core/base-index.ts, exercised transitively via Index / RangeIndex.
  • Assertion-level: src/stats/xs.ts honours the full pandas.{DataFrame,Series}.xs option surface, but the existing tests only covered the happy path with positive integer levels. Several supported behaviours had zero coverage.

Gaps closed in tests/stats/xs.test.ts (+19 cases, no production change)

  • Level addressing — named levels (level: "letter"), negative indices (level: -1), and the corresponding error paths (out-of-range number, unknown name) for both DataFrame and Series.
  • dropLevel: false — verifies the matched level and its name survive in the result MultiIndex, for both DataFrame and Series.
  • 3-level MultiIndex — xs at outer / middle / inner level, asserting the remaining level names land in the correct order (the only place the droplevel-of-arbitrary-position logic is observable).
  • Series name preservation on the duplicate-label branch.

Result

Coverage of src/stats/xs.ts rises from 76.92% → 92.31%; suite goes 6,765 → 6,784 tests, all green. The same audit pattern (probe the implementation's option surface against pandas docs, pin each branch) is the template to apply to the rest of the ported surface in follow-up PRs.

Copilot AI changed the title [WIP] Deep dive into pandas test coverage for ported functions Deep dive: pandas test parity audit — fill xs test coverage gaps Apr 30, 2026
Copilot finished work on behalf of mrjf April 30, 2026 23:01
Copilot AI requested a review from mrjf April 30, 2026 23:01
@mrjf mrjf marked this pull request as ready for review May 1, 2026 16:50
…errors

- Replace string-literal property access rec["size"], rec["at"], rec["getLoc"]
  with dot notation in src/core/frame.ts
- Refactor applyNearest in src/core/reindex.ts into three smaller helpers
  (buildLeftNearest, buildRightNearest, pickNearest) to bring cognitive
  complexity below the Biome limit of 15

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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github-actions Bot commented May 1, 2026

Commit pushed: 5762d43

Generated by Evergreen — PR Health Keeper

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github-actions Bot commented May 1, 2026

Evergreen fix applied — resolved the Test & Lint CI failure.

Root causes:

  1. src/core/frame.ts:782-784 — Biome lint/complexity/useLiteralKeys: replaced rec["size"], rec["at"], rec["getLoc"] with dot-notation (rec.size, rec.at, rec.getLoc).
  2. src/core/reindex.ts:159 — Biome lint/complexity/noExcessiveCognitiveComplexity: applyNearest had a complexity score of 24 (max 15). Refactored by extracting three focused helpers — buildLeftNearest, buildRightNearest, and pickNearest — bringing applyNearest well under the limit with no behaviour change.

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Generated by Evergreen — PR Health Keeper · ● 783.2K ·

…t TS compliance

- frame.ts: use rec["size"], rec["at"], rec["getLoc"] to satisfy noPropertyAccessFromIndexSignature
- reindex.ts: use ?? -1 / ?? null for noUncheckedIndexedAccess on array element access

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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github-actions Bot commented May 1, 2026

Commit pushed: cc70469

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github-actions Bot commented May 1, 2026

Evergreen CI Fix ✅

Fixed 4 TypeScript errors caught by tsc --noEmit:

src/core/frame.ts (lines 782–784): noPropertyAccessFromIndexSignature violation — used bracket notation rec["size"], rec["at"], rec["getLoc"] instead of dot access on Record<string, unknown>.

src/core/reindex.ts (line 208): noUncheckedIndexedAccess — array element access returns T | undefined; added ?? -1 for distances and ?? null for values (matching the existing -1/null sentinel pattern).

Generated by Evergreen — PR Health Keeper · ● 783.2K ·

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Deep dive -- are we accurately testing all our functions against pandas tests?

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