Basic test after file system hack

This post only for record the how to basic test after a file system hack

Dan Carpenter wrote:

On filesystem tests, you should always test them before submitting them. Everyone can create a small filesystem like this:

dd if=/dev/zero of=block bs=1M count=4000
mkfs.btrfs block mkdir mnt
sudo mount -o loop -t btrfs block mnt/ 

Maybe untar a kernel on it or something...
Not sure.
But if you mess up a filesystem people get annoyed. :P