At 22, wicketkeeper-batsman Samarawickrama is the youngest of the trio but has represented his country at the under-19 level.
Opener Kaushal Silva is back in the squad for the first time since January. The 31-year-old has not been called up since his first-ball duck against South Africa at the Wanderers on Jan. 14.
Lahiru Thirimanne will add experience to Sri Lanka’s batting lineup in the absence of the injured Mathews after being given the nod for the first time since the tour of England in June last year.
There was also a recall for seamer Suranga Lakmal, who missed the second and third tests against India last month with a back injury.
Sri Lanka will be hoping for a better showing in the two-test series with Pakistan after being whitewashed 3-0 by India at home last month, in what was one of the most one-sided test series of recent times.
The first test against Pakistan begins on Sept. 28. The second starts on Oct. 6 in Dubai and will be played in the new day-night format.
Squad: Dinesh Chandimal (captain), Lahiru Thirimanne, Dimuth Karunaratne, Kaushal Silva, Kusal Mendis, Sadeera Samarawickrama, Roshen Silva, Niroshan Dickwella, Rangana Herath, Lakshan Sandakan, Dilruwan Perera, Suranga Lakmal, Nuwan Pradeep, Vishva Fernando, Lahiru Gamage.
(Reporting by Simon Jennings in Bengaluru)