nunit-console: command not found

Have You tried accessing the binary with the full path?

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/nunit-console - from package: mono-nunit

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

On Debian possible default full paths are:

/usr/bin/nunit-console - from package: nunit-console

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