A kind of hidden room I found

[Prince Tuah]

I was running around in Arid Canyon Zone 2, and then running inside the minecart test room, which is hidden.
But just near the minecart test room when I go through a wall I found this room.
Anyone know about this room? Is it also some kind of test or unused platform? Or anything. And it's also appear to have black walls.

 

[RedSRB2]

I was running around in Arid Canyon Zone 2, and then running inside the minecart test room, which is hidden.
But just near the minecart test room when I go through a wall I found this room.
Anyone know about this room? Is it also some kind of test or unused platform? Or anything. And it's also appear to have black walls.

View attachment 98836

Most likely an unused room