Which of the following procedures will best help an internal auditor assess operating effectiveness of...

Testing is the most effective procedure for assessing the operating effectiveness of fraud prevention and detection controls. By testing specific controls designed to prevent and detect fraud, the auditor can evaluate whether the controls are functioning as intended and whether they are being applied consistently. This approach provides direct evidence about the effectiveness of the controls in the operational environment.

IIA guidance on assessing controls; Auditing standards on testing control effectiveness.