To test the theory that shutdowns are occurring due to outdated purchasing requirements that have not been updated for changes in production techniques, the auditor should compare the parts needed based on the most current production estimates and the revised materials requirements plan (MRP) with the purchase orders generated from the system. This comparison will help identify discrepancies between what is needed and what is being ordered, highlighting whether the system is failing to update purchasing requirements correctly. This method directly addresses the suspected cause of the shutdowns and provides clear evidence for or against the auditor's theory.
Reference:
Institute of Internal Auditors (IIA), International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2310 - Identifying Information.