Using pytest_addoptions in a non-root conftest.py

I have a project that has the following structure:

Project/
|
+-- src/
|   |
|   +-- proj/
|       |
|       +-- __init__.py
|       +-- code.py
|       +-- tests/
|           |
|           +-- __init__.py
|           +-- conftest.py
|           +-- test_code.py
+-- doc/
+-- pytest.ini
+-- setup.py

The importable package proj lives under the src directory. Tests are installed along with it, in the proj.tests sub-package. The code, the tests themselves, and the installation all work fine. However, I have trouble passing options to the tests.

I have an option, --plots, that is defined in conftest.py (under Project/src/proj/tests/), which creates a .plots/ folder in the root folder and places some graphical debugging there:

# conftest.py
def pytest_addoption(parser):
    parser.addoption("--plots", action="store_true", default=False)

There are two different ways I'd like to have to run this test:

1. The first is from the command line, in the Project directory:

   $ pytest --plots
   
   

   This fails immediately with

   usage: pytest [options] [file_or_dir] [file_or_dir] [...]
   pytest: error: unrecognized arguments: --plots
     inifile: /.../Project/pytest.ini
     rootdir: /.../Project
   
   

   If I add the package directory, the run goes fine:

   $ pytest src/proj --plots
   ...
   rootdir: /.../Project, inifile: pytest.ini
   ...
   
   

   It also goes well if I specify the tests sub-directory:

   $ pytest src/proj/tests --plots
   ...
   rootdir: /.../Project, inifile: pytest.ini
   ...
   
   

2. The second way is to run the test function of the package itself. The test function is defined in Project/src/proj/__init__.py like this:

   # __init__.py
   
   def test(*args, **kwargs):
       from pytest import main
       cmd = ['--pyargs', 'proj.tests']
       cmd.extend(args)
       return main(cmd, **kwargs)
   
   

   The function is intended to be run after Project is installed like this:

   >>> import proj
   >>> proj.test()
   
   

   Generally, this works OK, but if I do

   >>> proj.test('--plots')
   
   

   I get the same error as usual:

   usage:  [options] [file_or_dir] [file_or_dir] [...]
   : error: unrecognized arguments: --plots
     inifile: None
     rootdir: /some/other/folder
   
   

   For this test, I ran python setup.py develop and then cd'dto/some/other/folder` to make sure everything installed correctly.

My goal is to have both options working correctly when I pass in the --plots command line option. It seems that I have found a workaround for option #1, which is to manually pass in one of the packages to pytest, but I don't even fully understand how that works (why can I pass in either src/proj or src/proj/tests?).

So the question is, how to I get pytest to consistently run my test package so that the correct conftest.py gets picked up? I am willing to consider just about any reasonable alternative that allows me to get the --plots option working consistently in both the source (running in a shell from Project) version and the proj.test() version.

---

For reference, here is my pytest.ini file:

# pytest.ini

[pytest]
testpaths = src/skg/tests
confcutdir = src/skg/tests

It doesn't appear to make any difference.

I am running with pytest 3.8.0, on Pythons 2.7, 3.3, 3.4, 3.5, 3.6 and 3.7 (in anaconda). In all versions, the results are reproducible.