NSScreenTest: 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/NSScreenTest - from package: gnustep-examples

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

On Debian possible default full paths are:

/usr/bin/NSScreenTest - from package: gnustep-examples

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

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