I test a number of things for leakage around the shop, cooling systems, radiators, ourselves, hydronic systems, etc. Nothing too fancy about it, seal up the ends, put a fill valve with a gauge, and pressurize. A bike pump works good. Just be sure not to over pressurize. I like to use a valve to allow the test item to sit awhile under pressure. If it leaks, put it under water and see where the air comes from. I do this with exhaust manifold sometimes to find internal cracks.