support conftest/ folders

What's the problem this feature will solve?

I'm tired of putting so much code in a single tests/conftest.py file.

Describe the solution you'd like

It'd be nice if I could expand conftest.py into a folder, like this:

tests/conftest/__init__.py    # loaded instead of conftest.py; imports from sibling modules
tests/conftest/fixtures.py
tests/conftest/setup.py

Alternative Solutions

I could create a different folder, like tests/lib/, add code there, and import that code from tests/conftest.py, but I'd prefer to keep the rest of the tests/ namespace free. For example, the way I organize my tests is identical to how I organize my code. If I have a source file lib/foo.py, I'll create tests for it in tests/lib/test__foo.py. If I used tests/lib/ to instead store setup code for the test suite, that would conflict with the above convention.

Start by locating pytest's conftest discovery and loading entry point, then review existing tests for conftest.py behavior. Evaluate how tests/conftest/init.py, fixtures.py, and setup.py would be discovered, including the replacement relationship with tests/conftest.py. Done means the folder form works with sibling imports and existing conftest.py behavior remains intact.