nunit-console2: 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

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-console2 - from package: mono-nunit

You may install the required package with command yum install {package}
Error in other languages:
nunit-console2: bevel nie gevind nie
nunit-console2: comandă negăsită
nunit-console2: comando não encontrado
nunit-console2: commande introuvable
nunit-console2: command not found
nunit-console2: käsku ei ole
nunit-console2: không tìm thấy lệnh
nunit-console2: komanda nerasta
nunit-console2: Kommando nicht gefunden.
nunit-console2: kommandot finns inte
nunit-console2: komut yok
nunit-console2: nie znaleziono polecenia
nunit-console2: níor aimsíodh an t-ordú
nunit-console2: no se encontró la orden
nunit-console2: no s'ha trobat l'ordre
nunit-console2: opdracht niet gevonden
nunit-console2: parancs nem található
nunit-console2: perintah tidak ditemukan
nunit-console2: príkaz nenájdený
nunit-console2: příkaz nenalezen
nunit-console2: команда не найдена
nunit-console2: командата не е открита
nunit-console2: 命令找不到
nunit-console2: コマンドが見つかりません