phpunit: 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/phpunit - from package: php-phpunit-PHPUnit

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

On Debian possible default full paths are:

/usr/bin/phpunit - from package: phpunit

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

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