Fake your IO so that you can *actually* test how your system behaves at runtime. [Jepsen](https://jepsen.io/) is a project that aims to increase the reliability of distributed systems. The [Sled simulation guide](https://sled.rs/simulation.html) that contains basic information about deterministic testing of distributed, message-based, event-driven, or actor systems. [MadSim](https://github.com/madsim-rs/madsim) is a [[Rust]] async runtime that patches out [[Tokio]] in order to perform deterministic simulation of a system.