sources_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 Debian possible default full paths are:

/usr/lib/plainbox-providers-1/checkbox/bin/sources_test - from package: plainbox-provider-checkbox

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

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