I used a static analysis code coverage tool to guarantee it was checking the logic, but I did not verify the logic checking myself. The biggest risk is that I have no way of knowing that I codified actual bugs with tests, but if that's true those bugs were already there anyways.

I'd say for what I'm trying to do - which is upgrade a very old version of PHP to something that is supported, this is completely acceptable. These are basically acting as smoke tests.