fix: fixed merge conflicts on component barrel

lib/game/components/board.dart

@@ -6,7 +6,6 @@ import 'package:pinball/game/game.dart';
 ///
 /// The bottom [Component]s are the [Flipper]s and the [Baseboard]s.
 /// {@endtemplate}
-// TODO(alestiago): Add [SlingShot] once provided.
 // TODO(alestiago): Consider renaming once entire Board is defined.
 class BottomGroup extends Component {
   /// {@macro bottom_group}
@@ -70,7 +69,15 @@ class _BottomGroupSide extends Component {
             Flipper.height,
           ),
     );
+    final slingShot = SlingShot(
+      side: _side,
+      position: _position +
+          Vector2(
+            (Flipper.width) * direction,
+            Flipper.height + SlingShot.size.y,
+          ),
+    );
 
-    await addAll([flipper, baseboard]);
+    await addAll([flipper, baseboard, slingShot]);
   }
 }

lib/game/components/components.dart

@@ -4,6 +4,7 @@ export 'board.dart';
 export 'board_side.dart';
 export 'bonus_word.dart';
 export 'flipper.dart';
+export 'initial_position.dart';
 export 'jetpack_ramp.dart';
 export 'joint_anchor.dart';
 export 'launcher_ramp.dart';

lib/game/components/initial_position.dart

@@ -0,0 +1,17 @@
+import 'package:flame_forge2d/flame_forge2d.dart';
+
+/// Forces a given [BodyComponent] to position their [body] to an
+/// [initialPosition].
+mixin InitialPosition<T extends Forge2DGame> on BodyComponent<T> {
+  /// The initial position of the [body].
+  late final Vector2 initialPosition;
+
+  @override
+  void onMount() {
+    super.onMount();
+    assert(
+      body.position == initialPosition,
+      'Body position is not equal to initial position.',
+    );
+  }
+}

lib/game/components/sling_shot.dart

@@ -33,18 +33,19 @@ class SlingShot extends BodyComponent {
   /// left.
   final BoardSide _side;
 
-  List<FixtureDef> _createFixtureDefs() {
-    final fixtures = <FixtureDef>[];
-
+  /// The size of the [SlingShot] body.
   // TODO(alestiago): Use size from PositionedBodyComponent instead,
   // once a sprite is given.
-    final size = Vector2(10, 10);
+  static final Vector2 size = Vector2(6, 8);
+
+  List<FixtureDef> _createFixtureDefs() {
+    final fixtures = <FixtureDef>[];
 
     // TODO(alestiago): This magic number can be deduced by specifying the
     // angle and using polar coordinate system to place the bottom right
     // vertex.
     // Something as: y = -size.y * math.cos(angle)
-    const additionalIncrement = 2;
+    const additionalIncrement = 3;
     final triangleVertices = _side.isLeft
         ? [
             Vector2(0, 0),
@@ -78,7 +79,7 @@ class SlingShot extends BodyComponent {
       );
     // TODO(alestiago): Play with restitution value once game is bundled.
     final kickerFixtureDef = FixtureDef(kicker)
-      ..restitution = 20.0
+      ..restitution = 10.0
       ..friction = 0;
     fixtures.add(kickerFixtureDef);
 

lib/game/components/wall.dart

@@ -26,7 +26,7 @@ class Wall extends BodyComponent {
 
     final fixtureDef = FixtureDef(shape)
       ..restitution = 0.1
-      ..friction = 0.3;
+      ..friction = 0;
 
     final bodyDef = BodyDef()
       ..userData = this

test/game/components/board_test.dart

@@ -45,10 +45,10 @@ void main() {
           await game.ready();
           await game.ensureAdd(bottomGroup);
 
-          final leftFlippers = bottomGroup.findNestedChildren<Flipper>(
+          final rightFlippers = bottomGroup.findNestedChildren<Flipper>(
             condition: (flipper) => flipper.side.isRight,
           );
-          expect(leftFlippers.length, equals(1));
+          expect(rightFlippers.length, equals(1));
         },
       );
 
@@ -59,8 +59,20 @@ void main() {
           await game.ready();
           await game.ensureAdd(bottomGroup);
 
-          final leftFlippers = bottomGroup.findNestedChildren<Baseboard>();
-          expect(leftFlippers.length, equals(2));
+          final baseboards = bottomGroup.findNestedChildren<Baseboard>();
+          expect(baseboards.length, equals(2));
+        },
+      );
+
+      flameTester.test(
+        'has two SlingShots',
+        (game) async {
+          final bottomGroup = BottomGroup(position: Vector2.zero(), spacing: 0);
+          await game.ready();
+          await game.ensureAdd(bottomGroup);
+
+          final slingShots = bottomGroup.findNestedChildren<SlingShot>();
+          expect(slingShots.length, equals(2));
         },
       );
     });

test/game/components/initial_position_test.dart

@@ -0,0 +1,66 @@
+// ignore_for_file: cascade_invocations
+
+import 'package:flame_forge2d/flame_forge2d.dart';
+import 'package:flame_test/flame_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pinball/game/game.dart';
+
+class TestBodyComponent extends BodyComponent with InitialPosition {
+  @override
+  Body createBody() {
+    return world.createBody(BodyDef());
+  }
+}
+
+class TestPositionedBodyComponent extends BodyComponent with InitialPosition {
+  @override
+  Body createBody() {
+    return world.createBody(BodyDef()..position = initialPosition);
+  }
+}
+
+void main() {
+  final flameTester = FlameTester(Forge2DGame.new);
+  group('InitialPosition', () {
+    test('correctly sets and gets', () {
+      final component = TestBodyComponent()..initialPosition = Vector2(1, 2);
+      expect(component.initialPosition, Vector2(1, 2));
+    });
+
+    test('can only be set once', () {
+      final component = TestBodyComponent()..initialPosition = Vector2(1, 2);
+      expect(
+        () => component.initialPosition = Vector2(3, 4),
+        throwsA(isA<Error>()),
+      );
+    });
+
+    flameTester.test(
+      'returns normally '
+      'when the body sets the position to initial position',
+      (game) async {
+        final component = TestPositionedBodyComponent()
+          ..initialPosition = Vector2.zero();
+
+        await expectLater(
+          () async => game.ensureAdd(component),
+          returnsNormally,
+        );
+      },
+    );
+
+    flameTester.test(
+      'throws AssertionError '
+      'when not setting initialPosition to body',
+      (game) async {
+        final component = TestBodyComponent()..initialPosition = Vector2.zero();
+        await game.ensureAdd(component);
+
+        await expectLater(
+          () async => game.ensureAdd(component),
+          throwsAssertionError,
+        );
+      },
+    );
+  });
+}

test/game/components/wall_test.dart

@@ -106,7 +106,7 @@ void main() {
       );
 
       flameTester.test(
-        'has friction',
+        'has no friction',
         (game) async {
           final wall = Wall(
             start: Vector2.zero(),
@@ -115,7 +115,7 @@ void main() {
           await game.ensureAdd(wall);
 
           final fixture = wall.body.fixtures[0];
-          expect(fixture.friction, greaterThan(0));
+          expect(fixture.friction, equals(0));
         },
       );
     });