How do you test different tubes?

Elizabeth is right.

NOS tubes in any quantity are all gone, used, and burned out, and have been since the 80's.

Only the Russians and Chinese have made tubes in any quantity since then.

The Russian tube factories are controlled by the Russian mobs, and tube types come and go. The Chinese tube quality is very "spotty".

Try and find what is the best of new tubes, and buy a lifetime supply!

One thing that is nice about tubes is that they can be very easily tested for quality control. Because of that used tubes are a very viable option. The market in used tubes is virtually unlimited.

Also, in my experience the price of tubes is distorted by collectors/hoarders. Certain tubes and brands are commanding very high prices when there are readily available alternatives at much lower costs. For example, Mullard or Telefunken 12ax7s compared to U.S. made "organ" grade equivalents.

One last point, the differences between high quality, properly functioning tubes is subtle, yet like most things audiophile related users describe the differences as huge and earth shattering.

I disagree that tube rolling is pointless. Even if you believe there are no longer any good old tubes available, there are usually several new tubes to try. There are no lending programs however and as already stated the only way is to buy and try. You can sell what you don't like. Just because you didn't like the sonic of a particular tube it does not mean it is a bad tube, just not your taste. I happen to believe you can get some good old tubes but the price is getting extremely high.

While there aren't any tube lending libraries there are tube dealers whom people have learned to trust like Jim McShane, Kevin Deal, Brent Jesse and others. They can't tell you which tubes you would like in your equipment but they test the tubes, stand behind them and can give you general guidance about what might work for you. Here's one thread that's a few years old but should give you someplace to start.

Andy at Vintage Tube Services has the real deal. The idea that there are no good NOS tubes out there is patently untrue. As Elizabeth indicated, many private sellers are offing ones they did not like, but the best dealers are getting ones through means others do not have.

The last place I would buy a tube is eBay FWIW. At least not at full price as you will need to sort them.