There is a test where they stick a small pill like monitor in your stomach. You wear a beeper on your waist for 48 hours and it records the acidity in your stomach. They then take the beeper away from you and print the graph. The pill finally gets out from the other end.
It is kinda invasive but may be worth knowing. I am sure nowadays we may have other tests.
At times you may have pH 6.2 when the acid secretion is dormant. You get worse symptoms after taking enzymes, ACV etc. That may actually be lack of acid. Most of the times when you have heart burn it is a sign of low acid. Also as in my case I took so many antacid that my heart burn got worse. The antacids also leaves you with a weak sphincter.