test_mpi_openmpi: 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/lib64/openmpi/bin/test_mpi_openmpi - from package: openmx-openmpi

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

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