Unit tests are a poor substitute for correctness. Many unit tests does not a strong argument make. Unit tests are typically inductive. Developer shows case A

Unit tests are a poor substitute for correctness. Many unit tests does not a strong argument make. Unit tests are typically inductive. Developer shows case A, B and C give the expected results for function f. God help us if our expectations are wrong. So, you're saying since A, B and C are correct therefore function f is correct. Well that may be, or maybe A, B and C are trivial cases, in other words, you've made a weak argument. 100% test coverage sounds like lazy management. Alas, the manager may have worked their way via social programming rather than computer programming. In such cases, better to say you have 110% test coverage.