What tests can I perform to verify the 'spiritual realm' exists?
What tests can I perform that verify that a present state universe will exist in the future, that will kill it all? None.
Unlike morbid, baseless science claims, man has always known about spirits, and they are part of the record. For example, demon possession. Even today, there are folks that work in that field. In Jesus day it was commonplace. Spirits were listed as kings even, in the early days after the flood. Before the flood, humans married em, apparently. Spiritual gifts are rampant in among Christians, they come with the territory, basically. Inspiration, and joy and hope, and good things from above are quite spiritual. So, it has been verified every which way, and back, over thousands of years, nay since the very garden of Eden.
Just get over the shock to they sytem, that science is out of the loop. It is stuck in a play pen for the severely challenged. It can't punch it's way out of a box. All proofs and verification of anything spiritual, and that would include the past and future, leave science in the lurch. It just sits there, pegged to the present state ground in chains, unable to go anywhere talking out the side of it's big mouth.
The only sensible stragegy, when dealing in so called science, kids, is to not believe a thing it says, or waste time listening to it. It spouts only godless gibberish, gobbleygook, and garbage. By it's very nature, it can do nothing else!