In Go, it turns testing into a game of “how do I make this stdlib function return an error”?

Error handling taking up 50% of the code is definitely a problem with Go itself. For each meaningful line, there's an accompanying "if err != nil {return err}", so if you want coverage you end up testing this kind of boilerplate.

A trivial example would be getters and setters for plain old classes.

Surely the getters and setters of POJOs would be exercised in the tests of other classes? If not, why are they there?

E.g. it’s public api in a library and they’re only used by other applications.