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

Yes.

A developer writes the unittest te ensure that the "unit" does what it suppose to do. A QA person test the whole application.

Besides, a unit test is code, and developers write code. Most of the times QA engineers don't write code.