Questions about kidney health/function

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Age: 30 Duration: 3 years. Past medical: healthy

I started noticing dull pain sensation in left kidney every time after drinking alcohol starting 3 years ago. It was directly correlated to drinking alcohol as the symptoms were not present otherwise. Drinking has in my opinion been done in moderation however for the past 2-3 years I have stopped drinking altogether. There were however maybe 2 or 3 occasions when I was younger in which I drank to the point where I may have done some long term damage. Recently, slight twinges and pain sensations in both kidneys have come about recently even after not drinking alcohol. Questions are below:

I was not aware of kidney pain being related to alcohol, is this common?
Is it possible for 2 or 3 heavy drinking events to cause long term damage to kidneys or would it have to be an accumulation of heavy drinking over time?
What are the gold standard tests/exams to check for kidney function?
How are kidney donors tested to confirm they have healthy kidneys for transplants?
What are some tips to promote healthy kidney function?