i reckon it will be the same as that of any professional. in other words, human resources (HR) theory on recruitment and candidate selection would apply. how do you assess an engineer? there may be industry specific tests; at the same time, universal theory applying to any knowledge worker. HR theory stipulates how candidates can be evaluated
should have mentioned. these are the methods HR practitioners, etc commonly use:
interviews and follow-up interviews. from his language, etc it is already possible to determine whether the candidate knows his work.
assignments and tasks. the candidate is given small tasks etc to complete. from this it is also possible to gauge his skills.
probation. if the candidate pass the above, he is temporarily appointed to gauge his fit in the organization. at this point, his skill level would also be apparent