Add a test of asset locking and unlocking.

crates/bevy_asset/src/lib.rs

@@ -624,8 +624,8 @@ mod tests {
         },
         loader::{AssetLoader, LoadContext},
         Asset, AssetApp, AssetEvent, AssetId, AssetLoadError, AssetLoadFailedEvent, AssetPath,
-        AssetPlugin, AssetServer, Assets, DependencyLoadState, LoadState,
-        RecursiveDependencyLoadState,
+        AssetPlugin, AssetServer, Assets, DependencyLoadState, LoadState, MutableAssetError,
+        RecursiveDependencyLoadState, UnlockAssetError,
     };
     use bevy_app::{App, Update};
     use bevy_core::TaskPoolPlugin;
@@ -1548,6 +1548,55 @@ mod tests {
         assert_eq!(events, expected_events);
     }
 
+    #[test]
+    fn asset_locking() {
+        let mut app = App::new();
+        app.add_plugins(AssetPlugin::default())
+            .init_asset::<SubText>();
+
+        let mut assets = app.world_mut().resource_mut::<Assets<SubText>>();
+        let a = assets.add(SubText { text: "a".into() });
+        let b = assets.add(SubText { text: "b".into() });
+        let c = assets.add(SubText { text: "c".into() });
+
+        // Let everything propagate.
+        app.update();
+
+        let mut assets = app.world_mut().resource_mut::<Assets<SubText>>();
+        let a_arc = assets.lock(&a).expect("The asset exists");
+        let c_arc = assets.lock(&c).expect("The asset exists");
+
+        assert!(matches!(assets.get_mut(&a), Err(MutableAssetError::Locked)));
+        assert!(assets.get_mut(&b).is_ok());
+        assert!(matches!(assets.get_mut(&c), Err(MutableAssetError::Locked)));
+
+        // Aropping the Arc should allow us to unlock the asset.
+        drop(a_arc);
+        assert!(assets.try_unlock(&a).is_ok());
+
+        // The asset with the living Arc still cannot be unlocked or mutably accessed.
+        assert!(matches!(
+            assets.try_unlock(&c),
+            Err(UnlockAssetError::InUse),
+        ));
+        assert!(matches!(assets.get_mut(&c), Err(MutableAssetError::Locked)));
+
+        // Dropping the Arc should allow the asset to be automatically unlocked.
+        drop(c_arc);
+        app.update();
+
+        let mut assets = app.world_mut().resource_mut::<Assets<SubText>>();
+        // The asset was automatically unlocked!
+        assert!(assets.get_mut(&c).is_ok());
+
+        let b_arc = assets.lock(&b).expect("The asset exists");
+
+        assets.insert(&b, SubText { text: "d".into() });
+
+        assert_eq!(b_arc.text, "b");
+        assert_eq!(assets.get_mut(&b).expect("The asset exists").text, "d");
+    }
+
     #[test]
     fn load_folder() {
         // The particular usage of GatedReader in this test will cause deadlocking if running single-threaded