Inspections in the area of incoming goods and in the production are useful measures for quality assurance.
The exact procedure of the needed quality checks are defined in a list, the so called test plan.
Hereby the specification of the attributes (= what should be checked?), as well as the scope of testing (= how much should be tested?) is determined. Furthermore the test plan declares the time frame (= how often to check?) and the test equipment (= which device has to be used?).
If software based, known errors can be recorded in the test plan and measures defined to show what need to be done if defects appear.
The test plan provides, especially by adding descriptions and pictures, a comprehensive procedure to detect and respond to errors that might occured.