Solderability test can decide if your component solder terminations or your PCB can be soldered acceptably according to your requirements e.g. J-STD-002 (components) and J-STD-003 (PCB). A good/acceptable solder joint will wet onto the component termination and onto the PCB solder pad. With a poor solderability the solder will e.g. only wet on one part (PCB/component).
Today many components are bought via dealers around the world, and have maybe been stored in an inappropriate environment or might be an old date code, which can influence the solderability. Components and PCBs with poor solderability can decrease the reliability e.g. with hidden or latent defects in your products.
Solderability test can, for example, be used for examination and analysis of: