The following prescripts regarding the investigation about the qualities required in the one to be ordained are to be observed: 1/ there is to be a testimonial of the rector of the seminary or house of formation about the qualities required to receive the order, that is, about the sound doctrine of the candidate, his genuine piety, good morals, and aptitude to exercise the ministry, as well as, after a properly executed inquiry, about his state of physical and psychic health; 2/ in order to conduct the investigation properly, the diocesan bishop or major superior can employ other means which seem useful to him according to the circumstances of time and place, such as testimonial letters, public announcements, or other sources of information.
Source: Code of Canon Law (Vatican.va)