Toyota Repair: Electrical problem, battery cables, intermittent problem

Question
QUESTION: 94 Corolla 1.6L, 92000 mi 3 spd AT.  Recently the battery light started flickering.  Had the battery and alternator checked at 2 places, everything OK.  Removed and cleaned battery cables and  posts.  Starts and runs fine.  At night though, the headlights and dash lights will get very bright then dim down.  Any suggestions as to where to look for a problem?

ANSWER: The alternator may have an intermittent problem, I recommend replacing the alternator.

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QUESTION: Is there a specific test that can determine that for sure?

Answer
The alternator should be tested under load conditions with a tester that can apply an electrical load on the system while monitoring the voltage and amperage output, most of the time a mechanic will just put a voltmeter across the battery terminals to see what the voltage is with the engine at idle, this is not a reliable test as the alternator can break down as more current demand is put on it, like at night with all the lights and some accessories on.