Well, the premise stated above is that whatever testing you, the "author", judge sufficient doesn't matter; accuracy comes only at the hands of the sacred code review!
I dare you to review dense code for numerical computations and actually spot bugs. This is really hard! Unit tests are actually much more reliable but they are limited to deterministic algorithms and models that have reasonable complexity, that is, it is viable to compute expected results by alternate means.
Code review is more about determining if you have the correct test cases to cover the algorithm, and a solid architecture for maintenance, than it is about algorithmic correctness.
Code review is a tool to push back on your manager ignoring testing: “Steve requested I add X tests.”
