testland/dst-transition-reference
Pure-reference catalog of Daylight Saving Time (DST) transition patterns and their canonical bug classes. Covers the spring-forward (skipped hour: 02:00 → 03:00 local) and fall-back (repeated hour: 02:00 → 01:00 local) transitions, the historical irregularity of DST (different jurisdictions, transitions on different dates, some regions abolish DST or never adopted it), the IANA timezone database (tz / Olson DB) as the canonical source, and the testable behaviors DST creates (duplicate / missing local timestamps, cron jobs that fire 0 or 2 times, billing periods that miss / double-count, recurring meetings on transition days). Per-jurisdiction DST-rule tables, refreshable per-region test-data fixtures, and the leap-second reference (23:59:60 insertion, time_t stalls, leap-smear vs step, monotonic-clock fixes) live in references/. Use when designing or auditing time-handling code or test cases, or when auditing leap-second assumptions.
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jurisdictions-and-fixtures.mdreferences/
Per-jurisdiction DST rules and test-data fixtures
Deep reference for dst-transition-reference SKILL.md. Consult when
choosing which zones to cover and for refreshable per-region fixture
timestamps.
Per-jurisdiction differences
| Region | DST behaviour |
|---|---|
| US (most) | Spring-forward 2nd Sun March; fall-back 1st Sun November |
| EU | Last Sun March; last Sun October (one hour earlier) |
| Australia (most of NSW/VIC) | First Sun October; first Sun April (Southern hemisphere - reversed) |
| Australia (QLD, NT, WA, NT) | No DST |
| Japan, China, India | No DST |
| Russia | Abolished DST in 2011 |
| Iran | Abolished DST in 2022 |
| Mexico | Abolished mainland DST in 2022 |
| Brazil | Abolished DST in 2019 |
Per IANA: rules change frequently. Test against current zoneinfo, not assumptions.
Test data fixtures
Useful canonical timestamps per region (refresh against IANA):
| Region | Spring-forward 2026 | Fall-back 2026 |
|---|---|---|
| America/New_York | 2026-03-08 02:00 → 03:00 EDT | 2026-11-01 02:00 → 01:00 EST |
| Europe/London | 2026-03-29 01:00 → 02:00 BST | 2026-10-25 02:00 → 01:00 GMT |
| Australia/Sydney | 2026-10-04 02:00 → 03:00 AEDT | 2026-04-05 03:00 → 02:00 AEST |
These dates change year to year (some); commit a current fixture and refresh annually.