Viel Glück !
good test = guter Test
Good luck with that = viel Glück damit
"Viel Glück"
In French, you can say "bonne chance pour ton test" to wish someone good luck on their test.
In Portuguese, you can say "Boa sorte na tua prova" to wish someone good luck on their test.
bad luck in German language mean[pech]
"Viel Glück Kinder" would be the right phrase.
Viel glück und bis bald ( wiedersehen)
German: Viel Glück French: Bonne chance Italian: Buona fortuna
"Glück" is the word you are looking for.
Viel Glück!
good luck- powodzenia