There should be no .egg-info directory in the repo (or anywhere). That's really old setuptools stuff. If we have to have an entry_points.txt file then it should be in a .dist-info directory for the code. In fact there should be no use of setuptools in our repo as it's too heavy-handed for what we need it for. We should be using flit_core or hatchling as a build back-end instead since we only have pure Python packages. I.e. no setup.py, only pyproject.toml.

Have you tried using the -p option with the directory containing the plug-in on PYTHONPATH (or some other way to get it on to sys.path)? The wording of https://docs.pytest.org/en/stable/how-to/writing_plugins.html#making-your-plugin-installable-by-others suggests it might not be necessary to define an entry point. It also has an example of how to use pyproject.toml and hatchling to package things up if it turns out we actually do have to provide an entry point.