Chosen Solution
I have recently had to replace my FCAM/Sensor assembly (my ear piece audio went out) and was able to use an app to test the proximity sensor but there is no such ability with the ambient light sensor. I move from a well light room to a dark room and don’t notice any difference but I never really payed any attention in the past so can’t really tell if this would be noticeable. Is there any way to test this? or even create a situation when where the shift in brightness should be clearly apparent?
Go to general-accessibility-display-accommodations. Look for Auto brightness toggle. Switch it off and on. Do this in a dark room. Screen should get dimmer with low light and vice versa. This is your test
There is a Auto brightness toggle in the settings accessibly display accommodation area. Toggle that on and off and it should change brightness automatically when switched back on.
The best way to test it is to make sure auto brightness is on, then when the brightness is all the way up, put the phone into sleep, put your finger over the sensor an wake up the phone. If it works, the screen should dim and get brighter when you remove your finger. (Do this in a bright room)
We just hold them under a bright light under the microscope and watch the screen dim or brighten as we move the phone to and from the bright light