dahdi_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 CentOS possible default full paths are:

/usr/sbin/dahdi_test - from package: dahdi-tools

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

On Debian possible default full paths are:

/usr/sbin/dahdi_test - from package: dahdi

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

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