feat: included initial ball body component

lib/game/components/ball.dart

@@ -0,0 +1,28 @@
+import 'package:flame_forge2d/body_component.dart';
+import 'package:flutter/material.dart';
+import 'package:forge2d/forge2d.dart';
+
+class Ball extends BodyComponent {
+  Ball({
+    required Vector2 position,
+  }) : _position = position {
+    // TODO(alestiago): Use asset instead of color when provided.
+    paint = Paint()..color = const Color(0xFFFFFFFF);
+  }
+
+  final Vector2 _position;
+
+  @override
+  Body createBody() {
+    final shape = CircleShape()..radius = 2;
+
+    final fixtureDef = FixtureDef(shape)..density = 1;
+
+    final bodyDef = BodyDef()
+      ..userData = this
+      ..position = _position
+      ..type = BodyType.dynamic;
+
+    return world.createBody(bodyDef)..createFixture(fixtureDef);
+  }
+}

lib/game/components/components.dart

@@ -0,0 +1 @@
+export 'ball.dart';

lib/game/game.dart

@@ -1,2 +1,3 @@
+export 'components/components.dart';
 export 'pinball_game.dart';
 export 'view/pinball_game_page.dart';

test/game/view/components/ball_test.dart

@@ -0,0 +1,72 @@
+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';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  group('Ball', () {
+    group('body', () {
+      FlameTester(PinballGame.new).test(
+        'positions correctly',
+        (game) async {
+          final position = Vector2(10, 10);
+          final ball = Ball(position: position);
+          await game.ensureAdd(ball);
+
+          expect(ball.body.position, position);
+        },
+      );
+
+      FlameTester(PinballGame.new).test(
+        'is dynamic',
+        (game) async {
+          final position = Vector2(10, 10);
+          final ball = Ball(position: position);
+          await game.ensureAdd(ball);
+
+          expect(ball.body.bodyType, equals(BodyType.dynamic));
+        },
+      );
+    });
+
+    group('first fixture', () {
+      FlameTester(PinballGame.new).test(
+        'exists',
+        (game) async {
+          final position = Vector2(10, 10);
+          final ball = Ball(position: position);
+          await game.ensureAdd(ball);
+
+          expect(ball.body.fixtures.length, equals(1));
+        },
+      );
+
+      FlameTester(PinballGame.new).test(
+        'is dense',
+        (game) async {
+          final position = Vector2(10, 10);
+          final ball = Ball(position: position);
+          await game.ensureAdd(ball);
+
+          final fixture = ball.body.fixtures[0];
+          expect(fixture.density, greaterThan(0));
+        },
+      );
+
+      FlameTester(PinballGame.new).test(
+        'shape is circular',
+        (game) async {
+          final position = Vector2(10, 10);
+          final ball = Ball(position: position);
+          await game.ensureAdd(ball);
+
+          final fixture = ball.body.fixtures[0];
+          expect(fixture.shape.shapeType, equals(ShapeType.circle));
+          expect(fixture.shape.radius, equals(2));
+        },
+      );
+    });
+  });
+}