xrdp-sestest: 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/bin/xrdp-sestest - from package: xrdp

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

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