anchor.diff:            await game.ready();
   
             expect(
  -            () => game.children.singleWhere(
  -              componentSelector<BottomWall>(),
  -            ),
  -            returnsNormally,
  +            game.children.whereType<BottomWall>().length,
  +            equals(1),
             );
           },
         );
  
positive.code:     // [BallScorePointsCallback] once the following issue is resolved:
      // https://github.com/flame-engine/flame/issues/1416
      group('components', () {
        bool Function(Component) componentSelector<T>() =>
            (component) => component is T;
  
        flameTester.test(
          'has three Walls',
          (game) async {
            await game.ready();
            final walls = game.children
                .where(
                  (component) => component is Wall && component is! BottomWall,
                )
                .toList();
            // TODO(allisonryan0002): expect 3 when launch track is added and
            // temporary wall is removed.
            expect(walls.length, 4);
  
negative.code:         'has only one Plunger',
          (game) async {
            await game.ready();
            expect(
              game.children.whereType<Plunger>().length,
              equals(1),
            );
          },
        );
  
        flameTester.test('has only one FlipperGroup', (game) async {
          await game.ready();
          expect(
            game.children.whereType<FlipperGroup>().length,
            equals(1),
          );
        });
  
  