feat: enhanced component_controller

lib/flame/component_controller.dart

@@ -14,19 +14,18 @@ abstract class ComponentController<T extends Component> extends Component {
   /// The [Component] controlled by this [ComponentController].
   final T component;
 
-  /// Ads the [ComponentController] to its [component].
-  Future<void> attach() async {
-    // TODO(alestiago): check if component already attached.
-    await component.add(this);
-  }
-
   @override
-  Future<void> onLoad() async {
-    await super.onLoad();
+  Future<void> addToParent(Component parent) async {
     assert(
-      parent! == component,
+      parent == component,
       'ComponentController should be child of $component. '
       'Use attach() instead.',
     );
+    await super.addToParent(parent);
+  }
+
+  /// Ads the [ComponentController] to its [component].
+  Future<void> attach() async {
+    if (parent == null) await component.add(this);
   }
 }

test/flame/component_controller_test.dart

@@ -0,0 +1,63 @@
+// ignore_for_file: cascade_invocations
+
+import 'package:flame/game.dart';
+import 'package:flame/src/components/component.dart';
+import 'package:flame_test/flame_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pinball/flame/flame.dart';
+
+class TestComponentController extends ComponentController {
+  TestComponentController(Component component) : super(component);
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  final flameTester = FlameTester(FlameGame.new);
+
+  group('ComponentController', () {
+    flameTester.test(
+      'throws AssertionError when not attached to controlled component',
+      (game) async {
+        final component = Component();
+        final controller = TestComponentController(component);
+
+        final anotherComponet = Component();
+        await expectLater(
+          () async => await anotherComponet.add(controller),
+          throwsAssertionError,
+        );
+      },
+    );
+
+    group('attach', () {
+      flameTester.test(
+        'adds component controller to controlled component',
+        (game) async {
+          final component = Component();
+          final controller = TestComponentController(component);
+
+          await controller.attach();
+          await game.add(component);
+          await game.ready();
+
+          expect(component.contains(controller), isTrue);
+        },
+      );
+
+      flameTester.test(
+        "doesn't fail when already has a parent",
+        (game) async {
+          final component = Component();
+          final controller = TestComponentController(component);
+
+          await controller.attach();
+
+          await expectLater(
+            () async => controller.attach(),
+            returnsNormally,
+          );
+        },
+      );
+    });
+  });
+}