Control Testing involves auditors or compliance personnel executing procedures to gather evidence about whether controls function properly and prevent or detect errors and irregularities. Testing includes design evaluation (will the control work if performed?) and operating effectiveness (is it actually performed consistently?). For instance, testing a segregation of duties control requires examining whether the same person can both initiate and approve payments. Organizations perform control testing for financial reporting compliance (SOX 404), operational assurance, and regulatory requirements. Test results inform risk assessments, remediation priorities, and management's assertion about internal control effectiveness. Testing frequency and sample sizes depend on control criticality and historical performance.