his example of design by contract is silly out of functional testing. why would i even contact an external service/api if my own code can know what it will get

his example of design by contract is silly out of functional testing. why would i even contact an external service/api if my own code can know what it will get back every time? other than a side effect service, such as calling a disk IO and checking that return code means success, but then my check does not check anything...