I certainly had never heard of the two, until I looked into exorcising a werewolf. The best guess I have is that they are characters in literature but even of that I am not certain. The piece that I found about them was a comical look at exorcising a werewolf in which Gianni and Monna Tessa (also sometimes just called Tessa,) stand over a bed in order to remove the werewolf from a being or from the surroundings. Gianni says many prayers and makes signs of the cross over the bed while doing so. They then both chant this spell in order to make the exorcism complete:
“Fantasima, fantasima che di notte vai, a coda ritta ci venisti, a coda ritta te n’andrai: va nell’orto, a piè del pesco grosso troverai unto bisunto e cento cacherelle della gallina mia: pon bocca al fiasco e vatti via, e non far mal né a me né a Gianni mio.”
Translated to English this means:
“Werewolf, werewolf, black as any crow, you came here with your tail erect, keep it up and go; go into the garden, and look beneath the peach, and there you’ll find roast capons, and a score of eggs with each; raise the flask up to your lips, and take a swig of wine; then get you gone and hurt me not, nor even Gianni mine.”
This spell can be chanted to remove any evil beings but repeating the word ‘werewolf’ at the beginning makes it particularly effective against the hairy beasts. After having repeated the spell, one was also supposed to spit on the ground where the exorcism was completed although, whether or not these Gianni and Tessa characters do so, I’m not quite sure. But spitting was said to be a way of leaving your mark on the place where the spell was given.
And even though this piece between the characters was meant to be making fun of a fantasy world, the spell does come from actual spells. So if you know of a pesky werewolf in your neighborhood, you might want to give it a shot.