Integrated Test Facilities (ITF) are the most appropriate choice for simulating transactions for testing in an automated audit tool. ITF involves embedding fictitious transactions into the normal processing environment of the billing application without the knowledge of operational staff. This allows the internal auditor to assess transaction processing integrity, validation, and system calculations under real-time conditions.

Generalized audit software (GAS) is mainly used for data extraction and analysis but does not embed test transactions within live systems.

Utility software includes tools for system maintenance but is not designed for auditing transactions.

Audit expert systems provide decision-making support rather than transaction simulation.