mysql_client_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 CentOS possible default full paths are:

/usr/bin/mysql_client_test - from package: mysql55w-test
/usr/bin/mysql_client_test - from package: mysql-test

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

On Debian possible default full paths are:

/usr/bin/mysql_client_test - from package: mariadb-test-10.0
/usr/bin/mysql_client_test - from package: mysql-client-5.5

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

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