Testing. There are many occasions when testing is required but it broadly falls into two areas, development and production.
Development testing. Resources need to be available to make full use of prototypes. This is a good opportunity to check the CAD system bill of materials (BOM) as all components are purchased and built to it. By doing this, the product purchasing, part count and specification are checked at an early stage - valuable when there are long leadtime items to be ordered. All interfaces, form, fit and function are checked including electronics that can be in the form of printed circuit board (PCB) mock-ups with dummy connectors and wires. Sometimes, further prototype cycles are required via a design change to prove out any problems found. Sub-assembly or component tests are often setup to prove a specific element. Approval testing may also be carried out at this stage via an approved test house if certain standards have to be met.
Production testing. This is carried out wherever possible using early production components often mixed with prototype parts to supplement, depending on production part availability. This is used to validate design, purchasing and production. The whole product is finally checked and tested with all production parts for form, fit, function and conformity to required standards.