Self-Check Test Can Catch Game Simulation Bugs Before Multiplayer Desyncs Occur

Multiplayer game desyncs — where two clients diverge on game state — are notoriously hard to debug, but many originate from simulations that are not deterministic even on a single machine. A single-machine 'self-check' test can expose this by recording a session's inputs and tick hashes, replaying them, and comparing both recordings for any differences. Common culprits include randomized hash map iteration order, wall-clock time leaking into fixed-tick logic, uninitialized state, and persistent global variables across sessions. The open-source tool Tickwise automates this workflow and even ships with a chaos-injection flag to deliberately trigger known non-determinism for verification. Running this test before any networked play can eliminate an entire class of bugs without requiring a second machine, player, or live network connection.