Battery light flickering

When you tested the alternator did you just put the meter on the battery when the engine was running? Did you happen to load test the alternator?

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Basically the battery light coming on means that the PCM is seeing the voltage lower then the minimum threshold so it turns the light on.

Let me know if the alternator passes this type of test and we can go from there. You could at that point, have a wiring, voltage regulator, or PCM issue.