anchor.diff:            await game.ready();
   
             expect(
  -            () => game.children.singleWhere(
  -              componentSelector<BottomWall>(),
  -            ),
  -            returnsNormally,
  +            game.children.whereType<BottomWall>().length,
  +            equals(1),
             );
           },
         );
  
positive.code:         'has only one Plunger',
          (game) async {
            await game.ready();
  
            expect(
              () => game.children.singleWhere(
                (component) => component is Plunger,
              ),
              returnsNormally,
            );
          },
        );
  
        flameTester.test('has only one FlipperGroup', (game) async {
          await game.ready();
  
          expect(
            () => game.children.singleWhere(
              (component) => component is FlipperGroup,
            ),
            returnsNormally,
          );
        });
  
  
negative.code:         'has two Baseboards',
          (game) async {
            await game.ready();
            final baseboards = game.children.whereType<Baseboard>();
            expect(baseboards.length, 2);
          },
        );
  