Can just see a lot of info that DV has posted here that some may get mixed up or confused.
Fuel lines on the Nimrod are pressure tested with fuel not air, as you know air in a fuel system is not good
i posted my previous comments on how the system is tested and used a few examples to clarify what I was meaning not meant to be taken serious like brakes checked on car (it was example only)
If the fuel system has a leak you can smell , hear or visualise the leak.
im not aware of any other way of checking for leaks maybe using a pressure guage and having a noticeable drop might do the trick but that method is not used on the Nimrod.