Original: It is in the interest of the candidate to ascertain that the car they intend to use is insured for the purpose of taking the Taxi / Private Hire test as they will be required to sign a document to that effect.
Simplified: It is a good idea for the candidate to determine whether the car they will use is insured for taking the Taxi/Private Hire test. They will be required to sign a document that confirms the car is insured.