Vajrayana Buddhism is esoteric, in the sense that the transmission of certain teachings only occurs directly from teacher to student during an initiation or empowerment and cannot be simply learned from a book. Many techniques are also commonly said to be secret, but some Vajrayana teachers have responded that secrecy itself is not important and only a side-effect of the reality that the techniques have no validity outside the teacher-student lineage. (Source: http://en.wikipedia.org/wiki/Vajrayana#Esoteric_transmission)
But in my travels through the Buddhist landscape, I find that teachers are human: some good, some mediocre. How do I find the right teacher? Are there tests that the student can apply to the teacher?