We have that here at Firezone. To deal with I/O we don't use Tokio inside the test boundary at all, just futures. So no I/O, no sleeping, etc. Thomas explained it here https://firezone-git-docs-blogsans-io-firezone.vercel.app/bl...

I haven't dealt with it directly on Firezone but I wrote one or two games this way for game jams years ago, and I keep wishing it would catch on. It was harder with the games because floating-point math doesn't like to be deterministic across platforms.