There is a pragmatic perspective and a theoretic perspective. Pragmatically speaking, empirical methods can get one pretty far. It's better to have full cover

There is a pragmatic perspective and a theoretic perspective. Pragmatically speaking, empirical methods can get one pretty far. It's better to have full coverage of empirical tests across an entire system than limited coverage of formal tests, for instance. So, on that account, you may be correct from a pragmatic perspective. From an epistemological perspective, a test suite to confirm a property using chosen examples is not nearly as good as a formal proof that guarantees a property over a given domain. For simple cases, such as branch coverage, the test suite may be good enough. As complexity increases, or when testing things like modular arithmetic over an elliptic curve, unit testing leads to false confidence. But, just like in empirical testing, it's possible to build bad proofs. This is where the specialization comes in. There may be plenty of competent engineers who can hack at a test suite, but their results will not be nearly as comprehensive as someone trained in formal verification. It all comes down to epistemology. What do we know, and how do we know it? What possible defects exist in our system, and how bad can they be? Can we ship yet?