I have mostly worked in aerospace software, and find this rather horrifying. I suppose, if your tests are in fact good and comprehensive enough, there could be a logical argument for not needing to understand the code, but if we're talking people's safety in the hands of your software, I don't know if there is any number of tests I would accept in exchange for willingly giving up understanding of the code.
You're transferring the need to be really good at coding and understanding code to the need to be really good at testing and understanding tests, which 9/10 times requires being good at coding and understanding code. There are no free lunches.