Sample

Disprove the belief that fake-timer time seeding accepts arbitrary date strings.

sha256:143845512869b47a10e49289da6c1a5aa1c10b29acd92cd7bc7f166b4c5bbbae

Case

Goal

Disprove the belief that fake-timer time seeding accepts arbitrary date strings. HOW

Packages

jest 30.4.2

Environment

node

Created

2026-08-17T03:17:22Z

Commonly assumed

A strong implementation instinct is that `jest.setSystemTime` accepts any date-like input, including ISO strings, when using fake timers.

The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.

Contract

• Calling `jest.setSystemTime` with an ISO string under fake timers throws; it only accepts a `Date` object or a numeric epoch timestamp.
• After `jest.useFakeTimers()` and `jest.setSystemTime(new Date('2020-01-02T00:00:00.000Z'))`, `Date.now()` equals that date's epoch milliseconds.

Files

• NOTES.md
• csx.json
• package-lock.json
• package.json
• test/contract.test.mjs

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• node 22 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-17 · ed25519:d91480838ac982c9