my agent bulk-updated snapshots in CI where the timezone differed, baking the wrong timezone into every snapshot

Snapshots containing dates or times are only valid from the timezone they were recorded in. The agent regenerated them on a CI machine with a different timezone, so every stored value is now wrong. Revert the snapshots, pin the timezone explicitly in the test setup, and regenerate once on the pinned value.

my agent bulk-updated snapshots in CI where the timezone differed, baking the wrong timezone into every snapshot

Steps

1. Confirm the damage: search the updated snapshots for date and time strings and compare a few against the committed versions. The diff should show timezone offsets shifting, not real content changes.

   Expected: You can point at snapshot lines where only the timezone offset moved.

2. Revert every snapshot the bulk update touched, using version control. Do not try to hand-fix them; the committed versions are the source of truth.

   Expected: The snapshot files match the last known-good commit again.

3. Pin the timezone explicitly in the test setup: set the TZ environment variable (usually TZ=UTC) in the CI job, in the local test script, and in any test setup file that runs before the suite.

   Expected: Running the suite twice on different machines produces identical date output.

4. Regenerate the snapshots once, on a machine with the pinned timezone, and verify the diff against the reverted files contains only the changes you intended.

   Expected: The regeneration diff is clean: no timezone-only changes anywhere.

5. Make the timezone part of the checked-in config, not tribal knowledge: put TZ in the CI workflow file, the package test script, and a comment in the test setup file.

   Expected: A new contributor running the suite gets the same snapshots on the first run.

Use this when

• snapshot diffs show timezone offsets shifting after a CI bulk update
• an agent regenerated snapshots on a machine with a different timezone
• date strings in snapshots are wrong in a way that smells like TZ, not data

Not for this skill when

• the code under test has a real timezone bug (fix the code, not the snapshots)
• snapshots contain no dates or times at all
• only one snapshot changed and it is a genuine content change

Variant phrasings

• snapshots baked with wrong timezone after bulk update
• agent updated snapshots in CI with different timezone
• timezone offset in snapshots after regenerating in CI

Why it happens

Most test setups inherit the timezone from the machine they run on. A developer in one timezone records snapshots with local times baked in; CI in another timezone renders the same components with different offsets. When the agent bulk-updates snapshots on the CI machine, it overwrites the good values with wrong-timezone values, and now the snapshots are green in CI but wrong everywhere else. The timezone was never part of the test contract, so nothing flagged the switch.

Edge cases

• Daylight saving transitions can make the same pinned timezone produce different offsets across the year; UTC sidesteps this entirely.
• If the product genuinely shows local times, test that with explicit timezone fixtures per test rather than relying on the machine default.
• Docker-based CI often defaults to UTC while developer laptops do not; check both before blaming the agent.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstLZOLAazWks-9CGJ4MBJTg