mate-panel-test-applets: 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 Debian possible default full paths are:

/usr/bin/mate-panel-test-applets - from package: mate-panel

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