Go's synctest - deterministic concurrency tests
synctest gives concurrent Go tests a fake clock and a way to wait until every goroutine in a bubble is blocked.
This kills the worst pattern in Go testing: time.Sleep(100 * time.Millisecond) scattered through tests to “let things settle”. Those sleeps make suites slow and flaky at the same time - too short on a loaded CI runner, too long everywhere else.
With synctest a one-hour timeout test runs instantly and deterministically, because the clock only moves when nothing is left to do.
See also: