Sri Caitanya-caritamrta Madhya-lila 24.330, Lord Caitanya Mahaprabhu instructions Srila Sanatana Gosvami:
“Your book should describe the characteristics of the bona fide guru and the bona fide disciple. Then, before accepting a spiritual master, one can be assured of the spiritual master’s position. Similarly, the spiritual master can also be assured of the disciple’s position. ….”
As far as the mutual testing of the spiritual master and disciple is concerned, Srila Bhaktisiddhanta Sarasvati Thakura explains that a bona fide disciple, must be very inquisitive to understand the transcendental subject matter.
As stated in Srimad-bhagavatam (1 1.3.21):
“One who is inquisitive to understand the highest goal and benefit of life must approach a bona fide spiritual master and surrender unto him.”
A serious disciple must be alert, when selecting a bona fide spiritual master. He must be sure that the spiritual master can deliver all the transcendental necessities.
The spiritual master must observe how inquisitive the disciple is, and how eager he is to understand the transcendental subject matter.
The spiritual master should study the disciple’s inquisitiveness, for no less than six months or a year.”