RED: test gutter game

lib/bowling_game.dart

@@ -0,0 +1,9 @@
+class BowlingGame {
+  void roll(int pins) {
+    throw UnimplementedError();
+  }
+  
+  int score() {
+    throw UnimplementedError();
+  }
+}

test/bowling_game_test.dart

@@ -0,0 +1,16 @@
+import 'package:tdd_katas/bowling_game.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Bowling Game', () {
+    test('gutter game - all zeros', () {
+      final game = BowlingGame();
+
+      for (int i = 0; i < 20; i++) {
+        game.roll(0);
+      }
+
+      expect(game.score(), 0);
+    });
+  });
+}