message_bus | A reliable and robust messaging bus for Ruby and Rack | Data Migration library

From looking at this, looks like you're using a global variable which connects to something. Persistent connections are bound to an event loop. So if you want to continue using a global variable, the scope of the event loop fixture needs to match the scope of this variable.

I would redefine the event loop fixture to be session scoped, and create a session scoped fixture, depending on the event loop fixture, to initialize this global variable (by just calling get_bus, I suppose). The second fixture is required to ensure proper initialization ordering - i.e. that the event loop is set up properly first.

Edit: The documentation of pytest-asyncio says that event loops by default are test function scoped. Thus, they are being recreated in for each test. This default behavior can be simply overridden: