Final answer:
Auditing a sample of voucher entries tests the existence or occurrence assertion to confirm that the purchases transpired and supporting documents are valid.
Step-by-step explanation:
When an auditor vouches a sample of entries in the voucher register to the supporting documents, this procedure is most likely designed to support the existence or occurrence assertion. The auditor is seeking verification that the purchases recorded in the voucher register actually happened and that the supporting documents exist to validate each transaction.
This process involves checking whether the vouchers have indeed corresponded to real, tangible transactions and are not merely fabricated entries. Through this procedure, auditors can enhance the reliability of the financial statements by affirming that the recognized transactions have a basis in reality, akin to verifying the existence of a container of milk in a refrigerator. This tangible proof is essential for auditing standards.