DriveTime CLI (drivetimed-cli) - the disk surface test on a terminal (from StorageDiag Workbench & Utilities)

Pick the file for your NAS's CPU (uname -m): x86_64, aarch64, armhf or armel. Copy it to the NAS, then over SSH as
admin:

  chmod +x drivetimed-cli-x86_64
  ./drivetimed-cli-x86_64             pick a disk, watch or start its surface test
  ./drivetimed-cli-x86_64 --help      every command (probe, probe-ui, status, flags ...)

A test keeps running when you leave the screen with q. It reads the disk; it does not write to it.
Static binaries, nothing to install. Unofficial software, not a QNAP product.