Surprisingly, I haven’t been able to find any. Consumer Reports hasn’t done it, AFAICT. It’s all well and good for manufacturers to rate their clamping voltage and how many joules they can absorb, but it nobody is actually checking these claims, whom can we trust?
I think the better brands will mostly have UL ratings on them.
Does UL actually test the surge the suppression claims, or just confirm that they’re safe (i.e. won’t electrocute someone or cause a fire)?
UL-1449 is described as a safety and performance standard, so it appears they test both.
From UL-1449:
1.11 These requirements do not evaluate the effect of SPDs on connected loads, the effect of SPDs on harmonic distortion of the supply voltage, the degree of attenuation provided by SPDs, nor the adequacy of the voltage protection rating of SPDs to protect specific connected equipment from upset or damage.
Since it costs $716 to download the actual document, I’m unable to determine whether they test all to the same standard, or each to its published specs.
Sorry, that’s all I got 
How recent? Wirecutter did a review and updated it about 10 months ago. They do describe how they performed their testing.
I’m more concerned about the safety of those cheap power strips. Some of which, of course, have surge protectors.
Since USB ports is becoming an expectation with power strips. And since there’s a lot of “creativity” in implementing the USB standards (even just for power/charging purposes). Does UL also have a standard for that?
Of course, one sees all the time cheap stuff online that says “UL Approved” on them that no doubt is nothing but a label.
I had actually seen that article but for some reason dismissed it, but thanks, that appears to be the best that’s currently out there, and allowed me to make my decision.