Selenium login test doesn't accept pytest fixtures for login or refuses to connect

Turning the comment into an answer: by default, the tests avoid running db queries to not to slow down the test run, so User.objects.create_user doesn't write to database. To ensure db commits, use the @pytest.mark.django_db(transaction=True) marker in tests or the transactional_db fixture in your fixtures:

@pytest.fixture()def create_staff_user_in_db(transactional_db):    staff_user = User.objects.create_user(...)    ...

I assume that the live_server fixture of django uses transactional_db automatically but that the test_server doesn't?

Exactly - live_server implies the transactional mode, but the custom impl of test_server doesn't. Explicitly requesting the transactional_db fixture in test_server should fix it:

@pytest.fixturedef test_server(request) -> LiveServer:    request.getfixturevalue("transactional_db")    ...

BTW if you just want to apply the live server address dynamically, you shouldn't need to define your own fixture; writing config values should suffice. Example:

# conftest.pydef pytest_configure(config):    config.option.liveserver = socket.gethostbyname(socket.gethostname())

This value will then be used by the builtin live_server fixture. Put the conftest.py into your project or tests root dir to make pytest find the hookimpl early enough for it to be applied.