Test of design (ToD)
An assessment of whether a control, if it operated as described, would actually prevent or detect the failure it is meant to address.
Design testing asks a question that precedes any evidence of operation: would this control work, assuming it happens? A control performed diligently every month can still be badly designed — a review that does not include the population where errors occur, an approval by someone without the information to disagree, a reconciliation that would not detect the misstatement it is meant to catch.
It is normally performed through a walkthrough plus inspection of how the control is defined and what it produces. The output should be a statement about sufficiency, not a description of the process, and the most common weakness in audit files is exactly that substitution — pages describing what happens, with no conclusion on whether what happens is adequate.
Design is tested first for a practical reason: if the design is inadequate, operating effectiveness is irrelevant. A control that cannot work does not become effective by being performed on time.
Related