ztest: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/ztest - from package: zfs-fuse

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/bin/ztest - from package: zutils

You may install the required package with command apt-get install {package}

Error in other languages:
ztest: bevel nie gevind nie
ztest: comandă negăsită
ztest: comando não encontrado
ztest: commande introuvable
ztest: command not found
ztest: käsku ei ole
ztest: không tìm thấy lệnh
ztest: komanda nerasta
ztest: Kommando nicht gefunden.
ztest: kommandot finns inte
ztest: komut yok
ztest: nie znaleziono polecenia
ztest: níor aimsíodh an t-ordú
ztest: no se encontró la orden
ztest: no s'ha trobat l'ordre
ztest: opdracht niet gevonden
ztest: parancs nem található
ztest: perintah tidak ditemukan
ztest: príkaz nenájdený
ztest: příkaz nenalezen
ztest: команда не найдена
ztest: командата не е открита
ztest: 命令找不到
ztest: コマンドが見つかりません