mtdev-test: 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/mtdev-test - from package: mtdev-devel

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

On Debian possible default full paths are:

/usr/bin/mtdev-test - from package: mtdev-tools

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

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