```ruby
class Hanoi
  class Board
    def initialize(num_disks)
    end

    def towers
      [1, 2, 3]
    end
  end
end
```

Test update now fails correctly
user
```ruby
class Hanoi
  class Board
    def initialize(num_disks)
    end

    def towers
      [1, 2, 3]
    end
  end

  class Tower
  end
end
```
assistant