All of that can be done with automated tests, though agreed, they would not be (called) unit-tests (which are only used to prove how we've got our "perfect func

All of that can be done with automated tests, though agreed, they would not be (called) unit-tests (which are only used to prove how we've got our "perfect functions"). Of course, some of them could be unit-tests too (I've written small performance integration tests before, doing things like ensuring a function only ever emits a single SQL query, or timing execution and ensuring it scales in an O(1) manner, or ensuring data is passed by reference instead of being copied... where performance was a critical property of a "perfect function").