REFACTOR: break down the logic into dedicated methods, tests cleaned up

test/bowling_game_test.dart

@@ -2,7 +2,7 @@ import 'package:tdd_katas/bowling_game.dart';
 import 'package:test/test.dart';
 
 void main() {
-  group('Bowling Game', () {
+  group('Bowling Game Scoring', () {
     late BowlingGame game;
 
     setUp(() {
@@ -15,32 +15,64 @@ void main() {
       }
     }
 
-    test('gutter game - all zeros', () {
-      rollMany(20, 0);
-      expect(game.score(), 0);
+    group('Basic Scoring', () {
+      test('gutter game - no pins knocked', () {
+        rollMany(20, 0);
+        expect(game.score(), 0);
+      });
+
+      test('all ones - simple addition', () {
+        rollMany(20, 1);
+        expect(game.score(), 20);
+      });
     });
 
-    test('all ones - score is 20', () {
-      rollMany(20, 1);
-      expect(game.score(), 20);
+    group('Spare Bonus (next 1 roll)', () {
+      test('one spare in first frame', () {
+        game.roll(5);
+        game.roll(5); // spare
+        game.roll(3); // bonus for spare
+        rollMany(17, 0);
+
+        expect(game.score(), 16); // 10 + 3 (bonus) + 3
+      });
+
+      test('all spares with 5 pins each', () {
+        rollMany(21, 5); // 10 frames of 5,5 + 1 bonus roll
+        expect(game.score(), 150);
+      });
     });
 
-    test('one spare', () {
-      game.roll(5);
-      game.roll(5); // spare
-      game.roll(3); // bonus for spare
-      rollMany(17, 0); // rest are gutter balls
+    group('Strike Bonus (next 2 rolls)', () {
+      test('one strike in first frame', () {
+        game.roll(10); // Strike!
+        game.roll(3);
+        game.roll(4); // Next 2 rolls are bonus
+        rollMany(16, 0);
 
-      expect(game.score(), 16); // 10 (spare) + 3 (bonus) + 3 (normal roll)
+        expect(game.score(), 24); // 10 + 3 + 4 (bonus) + 7
+      });
+
+      test('perfect game - twelve consecutive strikes', () {
+        rollMany(12, 10);
+        expect(game.score(), 300);
+      });
     });
 
-    test('one strike', () {
-      game.roll(10); // Strike!
-      game.roll(3);
-      game.roll(4); // Next 2 rolls are bonus
-      rollMany(16, 0);
+    group('Complex Scenarios', () {
+      test('combination of strikes, spares, and normal frames', () {
+        game.roll(10); // Frame 1: Strike
+        game.roll(5);
+        game.roll(5); // Frame 2: Spare
+        game.roll(7);
+        game.roll(2); // Frame 3: Normal
+        rollMany(15, 0);
 
-      expect(game.score(), 24); // 10 + 3 + 4 (strike) + 3 + 4 (frame 2) = 24
+        // Frame 1: 10 + 5 + 5 = 20
+        // Frame 2: 10 + 7 = 17
+        // Frame 3: 7 + 2 = 9
+        expect(game.score(), 46);
+      });
     });
   });
 }