Sometimes quality personnel is given the daily task to verify the proper functioning of a leak testing system. Using a part with a known leak can be a good approach, as this checks the complete leak testing system. However, just using leaky parts from production or even purposely creating leaky parts (e.g. by drilling holes) is not a reliable option. Parts from production may change their leak rate over time (e.g. due to dirt from production getting to the leak path and clogging it or due to temperature changes). Also, it is very difficult to find or create a production part with a leak rate close to the reject leak rate.
A good way around this problem is to use a production part with an open style leak installed that has a leak rate equivalent to the reject leak rate. Open style leaks are very repeatable and come with a test leak certificate traceable to national standards. Using this approach offers the ability to test the complete testing process, e.g. also including whether the tools used for filling with tracer gas create a proper sealing on the part.