Your coffee analogy also says nothing about whether sugar or cream are better than one another, or if either is necessary.
Though I can guarantee you that either sugar or cream with only 0.1% coffee content will still be usable as sugar or cream for other purposes, so I can't even agree with your analogy taken to its limit: that no amount will make the coffee better, because enough will make it usable for other things.
In fact, unit testing and static type checking are largely orthogonal to the complecting issue that Rich was getting act. Unit testing and static typing will both increase complexity; they are both ways of making assertions about the behaviour of the code, and for working code, they should both actually be redundant. But that doesn't mean, as a practical issue, that we should do away with either or both. We're fallible. Saying the same thing twice or three times increases the probability of finding something inconsistent if our statements are not representative of the Platonic ideal we're trying to express.
Though I can guarantee you that either sugar or cream with only 0.1% coffee content will still be usable as sugar or cream for other purposes, so I can't even agree with your analogy taken to its limit: that no amount will make the coffee better, because enough will make it usable for other things.
In fact, unit testing and static type checking are largely orthogonal to the complecting issue that Rich was getting act. Unit testing and static typing will both increase complexity; they are both ways of making assertions about the behaviour of the code, and for working code, they should both actually be redundant. But that doesn't mean, as a practical issue, that we should do away with either or both. We're fallible. Saying the same thing twice or three times increases the probability of finding something inconsistent if our statements are not representative of the Platonic ideal we're trying to express.