test control of payroll system

For Problem 114, the answer to part b on page 241 BPP AA Kit:
Following is a control in answer:” The payroll supervisor selects a sample of payslips and recalculates the gross to net pay calculation, compares the results to the output from the payroll system and investigates any dicrepancies”
And the respective test of control in answer is: “For a sample of monthly payrolls reperform the gross to net pay calculation and compare to the payroll system, discussing any discrepancies with payroll supervior”
I want to ask, why the control is”..compares the results to the output from the payroll system and investigates any dicrepancies” but the test of control is still nearly the same, that is:”..discussing any discrepancies with payroll supervior”. I think it should be something like “For a sample of monthly payrolls reperform the gross to net pay calculation and compare to the payroll system, review the result of investigation of any disrepancies between output from the payroll system and the calculation of the gross to net pay calculation”
Please explain more to me about that!
Thanks!