ZAP-X is an innovative radiosurgery platform that is self-shielded, using gyroscopic motion to allow precision neurosurgical treatment. It requires a compact linac with lower than typical energy for medical applications. A 3 MeV S-band linac is designed and fabricated for this purpose. Thorough, clinical style testing was performed to verify the performance. The characteristics of photon beam, which is generated by the linac, are compared with the design goal, as well as Monte Carlo simulations.