Following tooling pre production prototypes will be produced. 

Prior to market release it is imperative to throughly test these to ensure that the product performs as intended.  A test procedure, based on the product requirements specification, should be prepared and the product tested thoroughly to ensure compliance.  Caught up in this will also be compliance testing to relevant standards and certifications such as CE mark, C tick, UL, TGA, etc requirements. 

Often accelerated life testing and environmental testing will be part of this process.  Sounds expensive and onerous?  Well, yes it is, but not compared to a rash of warranty claims or a safety recall.....