I'd argue that while they can't "do" their own testing, developers should be writing Unit tests that prevent their code from being broken in future. They shoul

I'd argue that while they can't "do" their own testing, developers should be writing Unit tests that prevent their code from being broken in future. They should also be writing tests that exercise their code so they find corner cases that were not obvious when coding. The problem is it's difficult to define what that is (and particularly to teach a junior Dev what to do).