testland/timezone-test-matrix-builder
Builds a timezone, daylight saving time (DST), and leap year / leap second test matrix from wherever a codebase reads or formats dates and times. Finds time-handling code (grep for datetime / Date / Instant / time.time / timezone), sorts each spot into storage, business-logic, display, cron, or billing, picks the edge cases that matter (DST spring-forward / fall-back, ambiguous local time, leap day Feb 29, ISO 8601 / RFC 3339 round-trip, zone-database updates), and emits per-spot test stubs wired to the language's fake-clock (mock-time) library. Use when a codebase needs timezone, DST, and leap-year test coverage derived from its own date/time usage.
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test-catalog.mdreferences/
Per-category test catalog
The test cases each touchpoint category should exercise. Pick the rows matching the category assigned during inventory (Step 1).
Storage tests
| Test | Pattern |
|---|---|
| Round-trip RFC 3339 | parse → emit → parse → assert equal |
| Round-trip via JSON | serialise object → deserialise → assert |
| Microsecond precision preserved | .123456Z survives DB store/load |
| Zone information preserved or normalized to UTC | Document the policy |
Business-logic tests
| Test | Pattern |
|---|---|
| DST spring-forward | Schedule at 02:30 local on transition day; verify behaviour |
| DST fall-back | Same 01:30 local appearing twice; verify ordering |
| Leap day Feb 29 | "1 year from Feb 29 2024" → Feb 28 2025 (Per ICU) |
| Year-end rollover | "Tomorrow" on Dec 31 |
| Month-end | Jan 31 + 1 month = Feb 28 / 29 (per library) |
| Negative durations | Operations on "5 minutes ago" |
| Leap second tolerance | Code uses monotonic time per leap-second-reference |
Cron tests
| Test | Pattern |
|---|---|
| Daily 02:30 EST cron on spring-forward | Doesn't fire OR fires at 03:30 (per cron spec) |
| Daily 01:30 EST cron on fall-back | Fires once vs twice (per spec) |
| Monthly on Feb 29 (non-leap year) | Fires on Feb 28 OR not at all |
| Weekly cron crossing DST | 1-hour offset for one week |
Billing tests
| Test | Pattern |
|---|---|
| Billing on month-end across leap year | Feb 28 vs Feb 29 handling |
| Billing window across DST | Hour gain / loss in the period |
| Pro-ration calculation | Across DST boundary |
| Multi-tenant timezone variance | Same wall-clock hour ≠ same UTC |
Display tests
| Test | Pattern |
|---|---|
| Per-user TZ formatting | User in Asia/Tokyo sees 09:00 JST; user in Europe/London sees 00:00 GMT |
| ISO 8601 vs human-readable | Localised display ≠ wire format |
| 24h vs 12h convention | Per user locale |
| Relative time ("2 hours ago") | Per system locale |