One - Why do you care how you got there? You need to read the code for that. But the tests do explain/document how you can expect the test to work. If the code is unreadable, well that sucks. But you at least have a programmatic (and hopefully annotated) description of how the code is expected to work, so you have a stable base for rewritting it to be more clear.

Two - Ever heard of code coverage? Type systems/type checkers? Also, there's nothing precluding you from using assertions in the test that make any assumed relations explicit before you actually test anything.