Ignore empty lines, comments when reading in packages_by_dep_dag.txt file

[jdavcs]

Also, add test; use session-scoped fixtures not to regenerate the same files for each test.

[mvdbeek]

Can you undo the session changes ? tmp_path is a python fixture, it is virtually free to create a temp dir for isolated tests. Also the pytest config looks weird to me, can you delete that too please ?

[jdavcs]

Thanks, the test is much simpler now. About pytest.ini - I mistakenly assumed I needed that for pytest to find the modules to import, which was not the case.