Game progression test cases, for the bug that loses the player

Save integrity is the category that matters most and is tested least. A crash during the write is not an exotic scenario on a mobile device: the operating system kills backgrounded apps routinely, batteries die, and players force quit. If the save is written in place, any of those produces a truncated file, and the next launch either crashes in a loop or starts the player from nothing. The fix is to write to a temporary file and swap it atomically, keeping the previous save as a fallback, and the test is simply to kill the process at the wrong moment and then load.

Cloud saves turn that into a distributed problem. Two devices played offline will both have legitimate progress, and one of them has to lose. There is no implementation that avoids the conflict, only implementations that handle it deliberately: apply a documented rule, and ask the player when the choice destroys something. Resolving by whichever write arrived last is the option that generates support tickets, because the player who lost four hours knows exactly what happened. The related case is the offline queue: replaying queued events on reconnection must not grant rewards twice or advance a counter twice.

Economy exploits come from state that persists inconsistently. The classic is a pickup whose currency is added immediately and persisted, while the pickup itself reverts on a checkpoint reload. Nothing errors, no rule is broken, and the loop can be repeated indefinitely. Once one player finds it, the whole economy is worthless within a week. The same reasoning applies to replaying a completed level for its first completion bonus, and to any client reported score accepted without a plausibility check.

Finally, purchases and timers are where trust is lost rather than fun. An entitlement restored from local data rather than from the platform receipt disappears on reinstall, and the player who paid is now asking support for a refund. A purchase interrupted mid transaction has to resolve to one definite state on relaunch, granting the entitlement if the platform actually charged and granting nothing twice. And every timer, regeneration and event window has to be evaluated against server time, because a device clock is player controlled input.