Fix a change detection test (#8605)

joseph-gio · web-flow · commit 1da726e046b3 · 2023-05-16T01:41:24.000Z
# Objective

The unit test `chang_tick_wraparound` is meant to ensure that change
ticks correctly deal with wrapping by setting the world's
`last_change_tick` to `u32::MAX`. However, since systems don't use* the
value of `World::last_change_tick`, this test doesn't actually involve
any wrapping behavior.

*exclusive systems do use `World::last_change_tick`; however it gets
overwritten by the system's own last tick in `System::run`.

## Solution

Use `QueryState` instead of systems in the unit test. This approach
actually uses `World::last_change_tick`, so it properly tests that
change ticks deal with wrapping correctly.
diff --git a/crates/bevy_ecs/src/change_detection.rs b/crates/bevy_ecs/src/change_detection.rs
@@ -814,24 +814,19 @@ mod tests {
 
     #[test]
     fn change_tick_wraparound() {
-        fn change_detected(query: Query<Ref<C>>) -> bool {
-            query.single().is_changed()
-        }
-
         let mut world = World::new();
         world.last_change_tick = Tick::new(u32::MAX);
         *world.change_tick.get_mut() = 0;
 
         // component added: 0, changed: 0
         world.spawn(C);
 
-        // system last ran: u32::MAX
-        let mut change_detected_system = IntoSystem::into_system(change_detected);
-        change_detected_system.initialize(&mut world);
+        world.increment_change_tick();
 
         // Since the world is always ahead, as long as changes can't get older than `u32::MAX` (which we ensure),
         // the wrapping difference will always be positive, so wraparound doesn't matter.
-        assert!(change_detected_system.run((), &mut world));
+        let mut query = world.query::<Ref<C>>();
+        assert!(query.single(&world).is_changed());
     }
 
     #[test]
