Draw a small state map
Start with only the states that exist today: ready, playing, paused, won, lost. List valid transitions such as ready to playing on Start, playing to paused on Pause, paused to playing on Resume, and playing to lost after a collision. Decide whether won or lost can transition to playing directly or must pass through ready. A tiny map exposes impossible routes before you add more screens or features.
Test duplicate and out-of-state input
Try the same transition twice quickly: double-click Start, press Pause twice, or hit Restart while the win panel is opening. Each state should handle repeated input deliberately instead of creating duplicate timers or overlays. Also press a gameplay key while paused or after losing. Decide whether the action is ignored, queued, or used by a menu, then verify the selected rule.
Questions about testing game state transitions
Which game states should I test first?
Cover the states that block play or end a run: ready, active play, pause, win or loss, and restart. Add intermediate screens when they change available actions.
Should gameplay input work while a pause menu is open?
Choose a rule and test it. Many games ignore movement while paused, but menu navigation may remain active; the important part is a consistent, visible distinction.