The sound test bug is a bug in The Final Fantasy Legend concerning the Sound Test and the attack "Sing".
The player can access the Sound Test by Holding Down, Start and the B button while on the title screen. They may need to hold them for a few seconds. Track 16 is not possible to hear outside of the Japanese version due to a bug. Since the attack for the song is associated with, "Sing", attempts to target everyone at once, it results in the attack affecting none of the targets and thus never actually doing anything.