There is a difference between unit tests and integration/ system/ component tests. I think the author is talking about pure unit tests, i.e. the ones that test

There is a difference between unit tests and integration/ system/ component tests. I think the author is talking about pure unit tests, i.e. the ones that test only one specific piece of code and mock everything else away. Too fine grained unit tests actually make refactoring more difficult, because a refactor typically touches so much code that they have to be rewritten. But component tests do provide the safety net that you had in mind when you wrote your reaction.