pg_prove: 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 Debian possible default full paths are:

/usr/bin/pg_prove - from package: libtap-parser-sourcehandler-pgtap-perl

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

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