Simplify configuration of session-scoped loops

[seifertm]

Pytest-asyncio users with a session-scoped event loop would have to add pytestmark = pytest.mark.asyncio(scope="session") for every package and subpackage to address the deprecation of event_loop fixture overrides (see discussion in #670).

This solution only applies to users that actually use test packages. Users that don't use test packages would have to add __init__.py files first or add pytestmark = pytest.mark.asyncio(scope="session") to each test module.

The goal of this issue is to have a more convenient way to configure session-scoped loops. Possible solutions:

• a configuration fixture
• a config option to set the default loop scope (mentioned previously, but I cannot find the reference)
• a config option to set the default test scope
• a pytest hook

[2e0byo]

What about the suggested collection hook solution in that issue? Hooks are bit weird, but copying a snippet from the documentation isn't the end of the world?

[seifertm]

I opted for your suggestion with the pytest hook.