That ^^ was my point - testnet is useless for high diff testing so only proves that fairly low diff (by today's standards) solutions are possible from new gear or code but at least testnet follows all of mainnets I/O and process requirements.
and lots of miners test equipment on testnet
Which only proves that the code & hardware does not crash and can handle lower diff scenarios. That leaves running/testing on the mainnet as the only way to ultimately prove something works.
Rolling your own private testnet that artificially forces very high diff target is another story. Should be possible but I'm unaware of anyone doing it, mainly because it would no longer be fully simulating main or test net protocols which leaves an uncertainty about it. Of course you would also be faced with the amount of time & hash power needed to produce the desired diff unless you do something to bias the code towards it but again that would entail breaking the normal protocols...
A better place to move this to would be the
Technical Discussion area where the folks are far better versed in this matter.
Right. In terms of "normal protocols" there's only Bitcoin and everything else. A Bitcoin miner is dumb and doesn't know what network it's on or even what "normal protocols" are. It only know how to solve one particular problem, whether on mainnet, testnet, or altcoin. Yet there's more nuance to mining on testnet than just proving if code and hardware doesn't crash and can handle lower diff scenarios. For example, one could test different builds of the same code, different batches of supposedly the same hardware, not to mention identifying the cause of any stubborn latency issues. There are many moving parts under the hood. And if one is seeing unusual patterns emerging in extremely large-scale miners, which is what I'm seeing, testnet or something similar could be used to understand what's causing them. Anyway, I think I know what to do. And I appreciate the feedback.