libguestfs-test-tool: 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/libguestfs-test-tool - from package: libguestfs

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

On Debian possible default full paths are:

/usr/bin/libguestfs-test-tool - from package: libguestfs-tools

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

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