Nice if you have them but not really required; loose, casual clothing or medieval-style garb is also common.

the normal clothing for witches and wizards; the robes always had a pocket for the wand; the Hogwarts students had black robes for school and dress robes for special occasions; Quidditch players wore Quidditch robes; a set of purple robes in the Black house tried to strangle Ron (OP6); dress robes were differently styled for witches and wizards (HBP6, 8)