Visa
Please follow this link on order to check country who needs a visa for entrance in Tunisia:
https://en.wikipedia.org/wiki/Visa_policy_of_Tunisia

Passport validity

For stays of up to 3 months your passport should be valid for the proposed duration of your stay; you don’t need any additional period of validity on your passport beyond this.

Departure tax

An exit tax of 30 dinars per person (about £11) now applies to all departing, non-resident foreigners.
You must buy an exit stamp before you leave Tunisia. You can buy the stamp at hotels, travel agencies, finance offices, tobacco shops, banks and customs offices (including at the airport and other borders). Payment is in cash in Tunisian dinars.
You can either fix the stamp into your passport next to the entry stamp yourself, or ask the border police to do it for you.