"small signal" tubes have very long lifespans when used in accordance with their design limits.
The design limits are readily available for most common tubes in RCA's fine series of
Receiving Tube Manuals.
Many different volumes thereof are easily available as (searchable) PDFs from the magnificient resource that is World Radio History.
Just go here and scroll down to the "Rs".
BOOKSHELF RCA: Radi Corporation of America tech guides
www.worldradiohistory.com
As an aside: the temptation to abuse tubes will be more typically found in power output sections. In the 1990s there was a company called Golden Tube Audio which was
notorious for the short lifespan of certain tubes in their amplifiers... due to the unsavory operating points they chose to use.
PS the best tube test for most tube types is the
in circuit use test. A properly calibrated transconductance type tube tester is invaluable for matching output tubes' operating characteristics (when that is necessary). Simple emissions-type testers do have their value, mostly for identifying grid leakage or shorts in a questionable tube. Full disclosure: the only tube tester I
own is a simple but reliable Sencore Mighty-Mite emissions tester which was my father's daily driver for decades
. It is "fit for purpose".
If I need to test a tube under actual operating conditions, I do know folks with proper transconductance testers. You might be surprised how easy it might be to find someone with a tube tester in your region. Look for amateur radio clubs or fleamarkets and ask around.