`test_cache_hit_flushes_the_index_once_the_window_has_passed` (from
#1544) failed on the first attempt of two of my PRs' Python Tests runs
today (#1576, #1579) and passed on rerun, with nothing in either PR
touching the image cache.
The test sets the clock to exactly `last_saved + ACCESS_FLUSH_SECONDS`
and expects a flush. `(now + 30) - now` isn't always 30.0 in floating
point. For example `105.65207077218265 + 30 - 105.65207077218265` is
`29.999999999999986`, so the `>=` check is false and the flush never
happens. That only shows up when the monotonic value is small, which
fits a freshly booted runner (on this box the uptime is in the millions
of seconds and it never fails). I haven't been able to see the runner's
actual uptime in the CI logs, so that part is an inference, but pinning
`_last_saved` to that value reproduces the exact failure (`assert [] ==
[1]`) locally.
The test now puts the clock one second past the window. The production
check is fine, real elapsed time doesn't have this edge, so only the
test changes.
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