What the dealer typically ends up doing is test drive the car at different speeds and try to determine based on sound if it is working well or not. If in that span of 3 minutes that they drive they do not hear anything then they wont really check any further. Same happens in the 60k maintenance when they are supposed to check the transmission, if there are no indicator lights going on, and they do not hear anything on a test drive then they will assume it is working well. Even when there might a failure, the procedure they have to go through according to manufacturer is a reset of the computer and maybe replace the transmission fluid.
I took my 2016 Corolla S Special Edition to the dealer on Saturday, they did not find anything wrong, but suggested a part needed to be replaced on the wheel and they would not look at the transmission until it was replaced because the tech suspected that was the source of the issue, their cost $700 ($250 for the part and over $400 for the labor). I took the car to a different shop that bought the part from a Toyota dealer for $58 and charged 1.5 hours labor for $90 {it was a wheel bearing and hub}. They gave me back the faulty bearing showing me there was actually nothing wrong with the bearing, and perfectly functional.
Here is what happened this morning while on my way to work:
Managed to limp back to a different dealer that happened to be close to where this happened, where the tech once again did not find a significant issue and considered the car drive-able but there might be a slight issue with the transmission.
CVTs are known for being very reliable, and with fewer moving parts compared to traditional automatic may have less chance of failure, but they are not immune to failure.