This ESR (equivalent series resistance) tester was built from an article by Lawrence - VE7IT.

This little tester was built and used to discover bad electrolytic caps. The caps were tested right on the circuit board, and you don't have to short the caps, prior to testing, for fear that you might damage your tester.

The meter movement was purchased from China (ebay) for $5. This shows a cap being tested. The meter reads 0 ohms, which indicates the cap is probably good.

I built a cardboard enclosure for it with my hot glue gun; inexpensive and quick.