gfxtest: 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/gfxtest - from package: gfxboot-dev

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

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