1. Tests designed to evaluate the machine/user interface. Are the communication device(s) designed in a manner such that the information is displayed in a understandable fashion enabling the operator to correctly interact with the system?

2. Usability testing is testing for 'user-friendliness'. Clearly this is subjective and depends on the targeted end-user or customer. User interviews, surveys, video recording of user sessions and other techniques can be used. Programmers and developers are usually not appropriate as usability testers.