This will be tested but unfortunately it is much harder to test it than just basic efficacy tests and it will take much more time. Like, in order to test that you have to have 1) someone vaccinated 2) that same person contracting COVID 3) confirming that that person has contracted COVID, 4) that person being in an environment where they can give COVID to other people, 5) determining if they ended up giving COVID to these people and 6) ascertaining that it was indeed them who gave the other people COVID. So that is a very non-trivial test. It is important though and I have even heard of some proposed tests to gather some volunteers and infect them on purpose after vaccinating them to see if they can transmit it to each other, how they cope etc. Which, like, sounds pretty scary and it will probably be some time before anything like that can happen, if it ever does. So it's not a trivial test and we shouldn't expect results like that to be confirmed any time soon.