It's a bit hard to test it precisely without pumping. But you could check that the pump is running and has suction.
Get a balloon and blow it up to Breast size, and then check that there is suction that pulls the balloon towards the breastshield funnel. Or put your hand over the breastshield and you should be able to feel suction at least.
Also check that the tiny white membrane disc is perfectly intact, with no rips, tears, or milk residue. That is the tiny part that controls the suction and often needs replacing.
Check this diagram which shows all the parts and the spares that we have available for you to order online: Swing Breast Pump Parts