Final answer:
The Research and Development (R&D) function is responsible for conducting customer tests and evaluating prototypes in the design and development step of the process development process.
Step-by-step explanation:
The function responsible for conducting customer tests and evaluating prototypes during the design and development phase of the process development process is Research and Development (R&D). Teams within R&D are directly involved with the testing and evaluation of prototypes, ensuring that the design meets all constraints and performs adequately relative to the established criteria. They work closely with designers and engineers to interface on testing materials, prototypes, and pre-production samples for manufacturing process implementation and production hand-off. Furthermore, R&D roles may include identifying and solving problems found through product and process testing, researching materials and specifications, designing and implementing tests, and involvement in every step from prototype development to finetuning the design for manufacturing.