I want to run my Python unit tests in a project. At the root the project contains a .arcconfig, a virtualenv directory 'venv' and some Python packages. (The stuff I care about).
I've added:
```"unit.engine" : "PytestTestEngine",```
to my .arcconfig - now when I run 'arc unit', in the project directory, it runs all unit tests in Python packages - but it also runs all the Python unit tests in the 'venv'.
I want to stop 'arc unit' from doing the latter. How do I do that?