The only causes for this condition are:
Faulty alternator
Faulty voltage regulator
Poor cable connections

Verify your connections both on the alternator and at the battery terminals. Insure they are tight and free of corrosion.

If all is well, you likely do have an issue with your alternator. The voltage regulator is internal to the alternator on your model. If the flickering were caused by the regulator, it would be due to abnormally high or low voltage output. This is not the case on yours, because if it were failed, you would not have passed any alternator tests.

Inside the alternator is also a diode pack; these diodes convert the AC (alternating current) voltage generated by the alternator into DC (direct current) voltage your car can use. A by-product of the diodes is always a trace amount of excess AC voltage present in the output. Excessive amounts of this AC voltage is what creates your flickering lights, nearly at all times the engine is running.

When you test the alternator, it is best to use a job-specific tester that is capable of testing the diode ripple. You can have a failing diode pack and still result in normal charging that on a basic tester would appear "OK"

Well.... you don't typically buy them for home use. Midtronics (midtronics.com) is probably one the better options out there, and is what I personally use. However a Midtronics that can test diode ripple is going to be in the 750-900$ range.

Your best bet to verify the condition is run by a dealership (most manufacturers require the dealerships have Midtronics or compatible level testers for just this purpose) and ask if they will do a full charging system test or a diode ripple test. They will likely charge you $29-50 depending on where you go, but it is much less than the cost of admission to buy one for yourself.

Verify the connections so you know it isn't anything simple, but traditionally these alternators have been know to have excess ripple issues from the diodes