Why in unit testing tests should not depend on the order of execution?

Question

It is a very often opinion that unit testing should not rely on tests order. I think it is not an exact rule but recommendation.

But in some cases it does not look good.

Answer 1

Because unit tests are meant to test individual units of work in isolation. Cutility method calls in CSoket should be mocked in unit tests for CSoket. This way, the unit tests for CSoket become independent of CUtility tests passing or failing. Then, it no longer matters if CUtility or CSoket tests are run first.