screentest: 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 Debian possible default full paths are:

/usr/bin/screentest - from package: screentest

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

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