Which test would you order for these painful vesicles?

A 43-year-old man presents with a two-day history of painful vesicles over the left side of the chin, cheek, ear and scalp, which subsequently became yellow-coloured and crusted.

Ramsay hunt syndrome

In addition, he reports shooting pain affecting the left side of the face and tongue.

He has also had tinnitus in the left ear and has noticed slight drooling from the same side.

He has no past medical history of note and takes no regular medications. He is given a trial of oral and IV antibiotics with no response.