An interesting way to visualize esr on a 'scope is to apply a bipolar square wave to it via a current limiting resistor, and look at the trace, an ideal cap would flat line, esr shows itself as a squarewave, the amplitude of which is proportional to esr.
Switching resistors enables you to change the current drive.
Another thing that can happen with caps is leakage, I have a cheap lashup using a neon, a cap and a resistor, the neon flashes at the rate of leakage, this is more usefull for vintage equipment repairs, I htink the circuit is copied right out of a piece of vintage test gear, besides a leaky cap is probably high esr anyway.