Where did you get that information???? I've never heard of a factory engine test using compressed air....
The lifter came in prefilled with fluid and then the factory installed them ..
They were sent down the line to a 'COLD TEST' stand where they spun the engine over by the crankshaft and measured different parameters... One of them was valve timing and they could tell if a lifter did not pump up fully... They called that a "soft lifter" and the engine would then be sent into the repair hole for the cold test, the offending lifter(s) replaced, and then the test was rerun...
In the old days they had a 'HOT TEST" where they fired up the engine and ran it for a few minutes....
