Unit tests by a QA Engineer

Question

As I understood from some Q&A sessions (see this and this), unit tests should be written by developers.

At my previous workplace we tried to give this task to a QA Engine

Answer 1

I don't think it would be bad, I just don't think it would be possible. If the code wasn't written test first it probably isn't testable.

Is the QA person doing to refactor the code to make it testable?

If so, then that's fine, and I don't care what their title is. If they're not, then I doubt they'll be successful.