Add tests for CircleShape

packages/forge2d/test/collision/shapes/circle_shape_test.dart

@@ -0,0 +1,27 @@
+import 'package:forge2d/forge2d.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('CircleShape', () {
+    test('Test radius', () {
+      const radius = 5.0;
+      final circleShape = CircleShape(radius: radius);
+      expect(circleShape.radius, equals(radius));
+    });
+
+    test('Test position', () {
+      final position = Vector2(1.0, 2.0);
+      final circleShape = CircleShape(position: position);
+      expect(circleShape.position, equals(position));
+    });
+
+    test('Test clone', () {
+      const radius = 5.0;
+      final position = Vector2(1.0, 2.0);
+      final circleShape = CircleShape(radius: radius, position: position);
+      final clonedCircleShape = circleShape.clone() as CircleShape;
+      expect(clonedCircleShape.radius, equals(radius));
+      expect(clonedCircleShape.position, equals(position));
+    });
+  });
+}