// waitForStopper stops the supplied util.Stopper and waits up to five seconds
// for it to complete.
func waitForStopper(t testing.TB, stopper *util.Stopper) {
stopper.Stop()
select {
case <-stopper.IsStopped():
case <-time.After(5 * time.Second):
t.Fatalf("Stopper failed to stop after 5 seconds")
}
}