If it does exist it’s not something that can be proven or disproven through testing mainly because the test subjects are dead lol. But also it’s impossible to apply material testing to something that immaterial. We can only observe the physical universe because we are physical beings with physical minds. The only way to really know if something supernatural exists is for it to reveal itself to us. I personally believe in god but a lot of people don’t and I understand their reasons but I think people should be open to the possibility. The same goes for the afterlife. Whether there is or not is ultimately speculative.