Blog post: Tests vs. time zones

[mrh-is]

See the PR: https://github.com/Kidfund/ios/pull/482

Storyline

• Write tests that differ by the value of a date
• Use date as part of filename for snapshots
• Tests are great, good job me
• Push
• CI servers don't like snapshot tests
• ???
• Oh, their filenames are different from the ones on my machine
• Oh, the hour is different
• Oh, looks like the time zone must be weird
• Try to fix by setting time zone to GMT for tests
• Fixes filename problem, but now the UI is wrong
  • Date formatter in UI uses default time zone
  • Tests think time is at midnight (GMT), UI thinks time is 7pm the night before
  • Tests technically pass, but they no longer test the real UX
• How to fix both?
• Just write time zone–insensitive data to filename!
  • That way, each machine can reinterpret it for its own time zone
• Change filename outputted to use protocol
• Add protocol conformance to Date
• Blammo, everyone's happy