mpitests-IMB-EXT: 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 CentOS possible default full paths are:

/usr/lib64/mpich/bin/mpitests-IMB-EXT - from package: mpitests-mpich
/usr/lib64/mvapich2-psm/bin/mpitests-IMB-EXT - from package: mpitests-mvapich2-psm
/usr/lib64/mvapich2/bin/mpitests-IMB-EXT - from package: mpitests-mvapich2
/usr/lib64/openmpi/bin/mpitests-IMB-EXT - from package: mpitests-openmpi

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