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Retesting Controls: – Its matter of professional judgement to decide whether to retest controls and what should be length of time between retesting / Even if there are no changes auditor should test controls once in every third audit. Shall test some controls each audit to avoid possibility of testing all controls in one audit.
As per SA 330 changes may affect the relevance of the audit evidence obtained in previous audits such that there may no longer be a basis for continued reliance. The auditor’s decision on whether to rely on audit evidence obtained in previous audits for control is a matter of professional judgment. In addition, the length of time between retesting such controls is also a matter of professional judgment.
If there have not been such changes, the auditor shall test the controls at least once in every third audit and shall test some controls each audit to avoid the possibility of testing all the controls on which the auditor intends to rely in a single audit period with no testing of controls in the subsequent two audit periods.

Factors affecting retesting on controls: –
Factors that may warrant a re-test of controls are-
Retesting should be done if there are “three Deficiencies in PM’s Computer”
Deficient Control Environment / Deficient General IT Controls / Deficient Monitoring on Controls / Personnel Changes / Manual Controls are Significant / Changing Circumstances.

• Deficient Monitoring of controls. (Purchases not covered in scope of Internal Audit)
• A deficient Control environment. (Poor attitude of management towards internal control system is encouragement to wrong doers)
• Deficient General IT-controls. (Purchase entries are ID restricted, but people use each other’s computer and they know username passwords)
• Personnel changes that significantly affect the application of the control. (Purchase & Store Manager Retired at the beginning of the year, they were replaced my new comers)
• A significant Manual element to the relevant controls. (Quotation Selection & Issuing PO is subjective matter and depends on approving authority, behaviour can change over period of time)
• Changing circumstances that indicate the need for changes in the control. (GST)