How do I create voltage ripple for the purpose of testing?
Use a power supply, with a small series resistor, going to the load under test, to provide the current.

Also going to the load under test, an 8 ohm resistor and a large capacitor in series, driven from an audio power amplifier, to provide the ripple.

Drive the amplifier input with your chosen ripple source, either real ripple, or create a wav with a simulator, and play it into the amplifier.