# Testing signals — date-fns/date-fns

> Canonical page: https://codevetter.com/unpack/date-fns/testing-signals

# Testing signals — date-fns/date-fns

Scanned commit 717ce0a807ea4c6b540d015b5c408723175b2838 (2026-09-22). Generated by codevetter codevetter 1.15.0 on 2026-10-02.

Source inspection; upstream code and tests were not executed.

Tests and CI were inspected, not executed; no passing status or coverage percentage is established. Vitest discovers package projects, with separate core main and Temporal-oriented suites and package-specific isolation settings. Inspected tests exercise mutation guarantees, invalid input, parsing boundaries, context types, DST gaps, and historical offsets. CI describes browser, Node-version, time-zone, smoke, type, lint, and locale checks, but this bounded inspection does not establish exhaustive coverage.
- Root Vitest discovers pkgs/*; core main includes src/**/test.ts, temporarily includes test.tp.ts, and both use forks, disabled isolation, concurrent sequencing, and optional Chromium via Playwright. — [vitest.config.ts#L1-L7](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/vitest.config.ts#L1-L7) [pkgs/core/vitest.config.ts#L7-L45](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/vitest.config.ts#L7-L45)
- addMonths tests assert timestamp support, input immutability, month-end clamping, pre-100 AD dates, invalid dates/amounts, UTCDate retention, and TZDate context inference. — [pkgs/core/src/addMonths/test.ts#L9-L49](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/addMonths/test.ts#L9-L49) [pkgs/core/src/addMonths/test.ts#L151-L180](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/addMonths/test.ts#L151-L180)
- Formatting tests cover quote escaping and formatDate alias behavior; parsing tests cover leap-day bounds, mismatches, invalid references, trailing whitespace, and unescaped-letter errors. — [pkgs/core/src/format/test.ts#L45-L69](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/format/test.ts#L45-L69) [pkgs/core/src/parse/test.ts#L2050-L2063](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/parse/test.ts#L2050-L2063) [pkgs/core/src/parse/test.ts#L2230-L2273](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/parse/test.ts#L2230-L2273)
- TZ tests include src/**/tests.ts and test/**/*.test.ts; inspected edge cases assert spring-forward normalization and historical second-offset behavior, while UTC configuration enables isolation. — [pkgs/tz/vitest.config.ts#L3-L10](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/tz/vitest.config.ts#L3-L10) [pkgs/tz/test/edge/new-york.test.ts#L13-L36](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/tz/test/edge/new-york.test.ts#L13-L36) [pkgs/tz/test/edge/historical.test.ts#L4-L26](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/tz/test/edge/historical.test.ts#L4-L26) [pkgs/utc/vitest.config.ts#L3-L10](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/utc/vitest.config.ts#L3-L10)
- Push/PR workflows invoke core Node, browser, and time-zone tasks; Node tests name versions 22/24/25/26, and the zone runner launches Vitest with TZ and VITEST_MAX_WORKERS=1. — [.github/workflows/node_tests.yaml#L3-L15](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/.github/workflows/node_tests.yaml#L3-L15) [.github/workflows/browser_tests.yaml#L18-L22](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/.github/workflows/browser_tests.yaml#L18-L22) [pkgs/core/scripts/test/node.sh#L7-L21](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/scripts/test/node.sh#L7-L21) [pkgs/dev/src/test/tz.ts#L407-L413](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/dev/src/test/tz.ts#L407-L413)
- Smoke CI delegates to example tasks; quality CI invokes type checking, linting, and locale snapshots, whose renderer covers format/parse, distances, relative dates, and durations under TZ=utc. — [.github/workflows/smoke_tests.yaml#L14-L15](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/.github/workflows/smoke_tests.yaml#L14-L15) [.github/workflows/code_quality.yaml#L14-L21](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/.github/workflows/code_quality.yaml#L14-L21) [pkgs/core/mise.toml#L115-L123](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/mise.toml#L115-L123) [pkgs/core/scripts/build/localeSnapshots/index.ts#L24-L50](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/scripts/build/localeSnapshots/index.ts#L24-L50)
- The inspected docs tests assert export/module-node classification and repository-path conversion; its npm test script is a deliberate failure placeholder despite a Vitest tests.ts configuration, so that script is not a reliable docs-suite entrypoint. — [pkgs/docs/src/data/tests.ts#L1-L29](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/docs/src/data/tests.ts#L1-L29) [pkgs/docs/vitest.config.ts#L3-L8](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/docs/vitest.config.ts#L3-L8) [pkgs/docs/package.json#L38-L40](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/docs/package.json#L38-L40)
- Coverage CI is workflow_dispatch-only with a TODO; addMonths DST cases are conditional on detected transitions, and inspected docs helper tests do not demonstrate Firebase publication/rollback verification. Tests and workflows were read, not run. — [.github/workflows/coverage.yaml#L3-L18](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/.github/workflows/coverage.yaml#L3-L18) [pkgs/core/src/addMonths/test.ts#L52-L55](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/core/src/addMonths/test.ts#L52-L55) [pkgs/docs/src/data/tests.ts#L1-L29](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/docs/src/data/tests.ts#L1-L29) [pkgs/docs/src/bin.ts#L34-L120](https://github.com/date-fns/date-fns/blob/717ce0a807ea4c6b540d015b5c408723175b2838/pkgs/docs/src/bin.ts#L34-L120)

Every claim links to its cited files at the pinned commit. Citations identify source evidence; they do not establish runtime correctness. Independent CodeVetter scan — not reviewed by upstream maintainers.

## Public product links

- [CodeVetter](https://codevetter.com/)
- [Download](https://codevetter.com/download)
- [Documentation](https://codevetter.com/docs/)
- [Source](https://github.com/Codevetter/codevetter)