bevy_ecs: add failing test for spawn-in-despawn-observer

Author: jrobsonchase

crates/bevy_ecs/src/observer/mod.rs

@@ -1160,4 +1160,23 @@ mod tests {
         world.flush();
         assert_eq!(vec!["event", "event"], world.resource::<Order>().0);
     }
+
+    #[test]
+    fn observer_on_remove_during_despawn_spawn_empty() {
+        let mut world = World::new();
+
+        world.observe(|_: Trigger<OnRemove, A>, mut cmd: Commands| {
+            cmd.spawn_empty();
+        });
+
+        world.flush();
+
+        let ent = world.spawn(A).id();
+
+        world.flush();
+
+        world.despawn(ent);
+
+        world.flush();
+    }
 }