my back passenger side brake has been leaking brake fluid does anyone know what it could be as i need to get it fixed before my test so i can get some practice in.

Depends exactly where the fluid is coming from. If its coming from inside the drum and is leaking out the bottom,it'll be the cylinder inside.

Could be coming from connection or nipple at the back,though. This you can tell easily,as it'll show up on the back plate.