Testing Across Timezones
Override the browser timezone to catch date/time display bugs, scheduling issues, and timezone conversion errors.
Date and time bugs are subtle and painful. A meeting shows at 3 PM for a user in London but 3 AM for someone in Sydney. An expiration date is off by one day across the date line. Certyn catches these by emulating different timezones.
How It Works
The agent uses Chrome DevTools Protocol's Emulation.setTimezoneOverride to change the browser's timezone. JavaScript's Date object, Intl.DateTimeFormat, and every other time-related API will behave as if the user is in that timezone.
This is more accurate than changing your OS timezone — it only affects the browser, and it happens instantly.
What to Test
Date displays
- Do dates format correctly for each timezone?
- Is "today" correct across the date line?
- Do relative dates ("2 hours ago") account for timezone?
Scheduling features
- Do calendar events show at the right time?
- Does "available at 9 AM EST" translate correctly for PST users?
- Are recurring events handled across DST boundaries?
Deadlines and countdowns
- Does a "ends at midnight" deadline work for all timezones?
- Are countdown timers accurate regardless of timezone?
Example Scenarios
Test appointment booking from Tokyo
"Set timezone to Asia/Tokyo and book an appointment for 2 PM. Verify the confirmation shows the correct Tokyo time."
Check date display near the date line
"Set timezone to Pacific/Auckland (UTC+12) and check if today's date shows correctly on the dashboard."
Verify timezone in notifications
"Set timezone to Europe/London and trigger a notification with a timestamp. Check it shows GMT, not the server's timezone."
Common IANA Timezone IDs
| Region | Timezone ID |
|---|---|
| US East | America/New_York |
| US West | America/Los_Angeles |
| UK | Europe/London |
| Central Europe | Europe/Berlin |
| Japan | Asia/Tokyo |
| Australia | Australia/Sydney |
| New Zealand | Pacific/Auckland |
| India | Asia/Kolkata |
Tips
- Always use IANA timezone IDs (like
America/New_York), not abbreviations (likeEST) - Test near DST transitions — this is where most bugs hide
- Combine with geolocation for a complete regional simulation
- Use empty string to reset back to the default timezone