fix: Add assertion when trying to set "current" that doesn't exist (#…

…3258)

Currently when setting `current` in `SpriteAnimationGroupComponent` and
`SpriteGroupComponent` we silently fail if the key isn't in the map.
This PR adds assertions so that we at least warn about it in debug mode.

packages/flame/lib/src/components/sprite_animation_group_component.dart

@@ -140,6 +140,12 @@ class SpriteAnimationGroupComponent<T> extends PositionComponent
   ///
   /// Will update [size] if [autoResize] is true.
   set current(T? value) {
+    assert(_animations != null, 'Animations not set');
+    assert(
+      _animations!.keys.contains(value),
+      'Animation not found for key: $value',
+    );
+
     final changed = value != current;
     _current = value;
     _resizeToSprite();

packages/flame/lib/src/components/sprite_group_component.dart

@@ -68,6 +68,9 @@ class SpriteGroupComponent<T> extends PositionComponent
   ///
   /// Will update [size] if [autoResize] is true.
   set current(T? value) {
+    assert(_sprites != null, 'Sprites not set');
+    assert(_sprites!.keys.contains(value), 'Sprite not found for key: $value');
+
     final changed = _current != value;
     _current = value;
     _resizeToSprite();

packages/flame/test/components/sprite_animation_group_component_test.dart

@@ -45,6 +45,16 @@ Future<void> main() async {
       component.current = _AnimationState.running;
       expect(component.animation, animation2);
     });
+
+    test('Asserts that map contains key', () {
+      expect(
+        () {
+          SpriteAnimationGroupComponent<String>(animations: {}).current =
+              'non-existent-key';
+        },
+        failsAssert('Animation not found for key: non-existent-key'),
+      );
+    });
   });
 
   group('SpriteAnimationGroupComponent.shouldRemove', () {

packages/flame/test/components/sprite_group_component_test.dart

@@ -34,6 +34,16 @@ Future<void> main() async {
       component.current = _SpriteState.running;
       expect(component.sprite, sprite2);
     });
+
+    test('Asserts that map contains key', () {
+      expect(
+        () {
+          SpriteGroupComponent<String>(sprites: {}).current =
+              'non-existent-key';
+        },
+        failsAssert('Sprite not found for key: non-existent-key'),
+      );
+    });
   });
 
   group('SpriteComponent.autoResize', () {