ttest: 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/cmtk/bin/ttest - from package: cmtk

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

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