The sidebar row's Tip trigger test derives its fixture from the wall clock:
const startedAt = Math.floor(Date.now() / 1000) - 5 * 60
...
expect(age.getAttribute('aria-label')).toMatch(/^5m, Today at /)
"Five minutes ago" is only today when the run does not straddle local
midnight. Between 00:00 and 00:05 the timestamp falls into the previous
day, formatMessageTimestamp correctly returns the yesterday label, and
the test fails on a day boundary it was never written to exercise:
AssertionError: expected '5m, Yesterday at 11:56 PM'
to match /^5m, Today at /
This is a real CI failure, not a theoretical one - it took down a
check:test:ui shard on an unrelated desktop PR at 00:01 UTC, and it will
do so for any PR whose shard happens to land in that five-minute window.
Pin the clock to local noon before deriving the timestamp so the fixture
can never cross a day boundary. Only Date is faked (toFake: ['Date']),
so the component's own timers - the running arc and the tooltip open
delay - keep running for real; the neighbouring tooltip tests that
advance timers are unaffected. The describe block gains the
useRealTimers teardown its sibling already had.
The production formatter is not changed: rendering "Yesterday at 11:56
PM" for a session started five minutes before midnight is correct, and
the assertion is about the label's composition, not about which day it
names.
a7b8281a16