network_bandwidth_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 Debian possible default full paths are:

/usr/lib/plainbox-providers-1/checkbox/bin/network_bandwidth_test - from package: plainbox-provider-checkbox

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

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