Add test

src/state.rs

@@ -46,6 +46,7 @@ impl SpriteSheetAnimationState {
                 self.current_frame = 0;
             } else {
                 self.current_frame = 0;
+                self.elapsed_in_frame = Duration::ZERO;
                 return true;
             }
 
@@ -371,6 +372,19 @@ mod tests {
             ) {
                 assert!(state.update(&mut sprite_at_second_frame, &animation, frame_duration))
             }
+
+            #[rstest]
+            fn returns_to_initial_state(
+                mut state: SpriteSheetAnimationState,
+                mut sprite_at_second_frame: TextureAtlasSprite,
+                animation: SpriteSheetAnimation,
+                frame_duration: Duration,
+            ) {
+                state.update(&mut sprite_at_second_frame, &animation, frame_duration);
+                let expected_state = SpriteSheetAnimationState::default();
+                assert_eq!(state.current_frame, expected_state.current_frame);
+                assert_eq!(state.elapsed_in_frame, expected_state.elapsed_in_frame);
+            }
         }
     }
 }