Immediate Execution of Commands on a &mut World

crates/bevy_diagnostic/src/execute.rs

@@ -24,7 +24,7 @@ impl Execute for &mut World {
     ///
     /// let mut world = World::default();
     /// let entity = world.execute(|_world, mut commands| {
-    ///     commands.spawn().id()
+    ///     commands.spawn(()).id()
     /// });
     ///
     /// assert!(world.get_entity(entity).is_some());

tests/how_to_test_commands.rs

@@ -0,0 +1,51 @@
+use bevy::{diagnostic::Execute, ecs::system::EntityCommands, prelude::*};
+
+#[derive(Component, Default)]
+struct Position(Vec2);
+
+#[derive(Component)]
+struct Destination(Vec2);
+
+trait NavigateTo {
+    fn navigate_to(self, target: Entity);
+}
+
+impl NavigateTo for &mut EntityCommands<'_, '_, '_> {
+    /// Start navigation for this [`Entity`] towards [`Position`] of `target`.
+    fn navigate_to(self, target: Entity) {
+        let entity = self.id();
+        self.commands().add(move |world: &mut World| {
+            // Get position from target
+            let &Position(xy) = world
+                .get::<Position>(target)
+                .expect("target must have a position");
+            // Set navigation destination
+            world.entity_mut(entity).insert(Destination(xy));
+        });
+    }
+}
+
+/* ... */
+
+#[test]
+fn did_set_destination() {
+    const TARGET_POS: Vec2 = Vec2::new(5.0, 2.0);
+
+    let mut world = World::default();
+
+    // Spawn entity
+    let entity = world.spawn(Position::default()).id();
+
+    // Spawn target at `TARGET_POS`
+    let target = world.spawn(Position(TARGET_POS)).id();
+
+    world.execute(|_world, mut commands| {
+        commands.entity(entity).navigate_to(target);
+    });
+
+    // Ensure destination is set correctly to position of target
+    let &Destination(destination) = world
+        .get::<Destination>(entity)
+        .expect("entity must have a destination");
+    assert_eq!(destination, TARGET_POS);
+}