Select which test should be distributed and which test should be run without concurrence

I would like to use pytest-xdist in mne-lsl: https://github.com/mne-tools/mne-lsl/pull/229
However, in the test suite, some test need to be run while no other test are running because they spawn network resources which might be pick-up by other tests. Example:

def test1(...):
    spawn_network_resources()
    ...

def test2(...):
    resources = resolve_all_network_resources()
    assert len(resources) == 0
    spawn_network_resources()
    resources = resolve_all_network_resources()
    assert len(resources) == 1

In this example, test2 would be affected by test1 run in a different worker.
To avoid this problem, I would like new markers from pytest-xdist to mark which test should not be distributed and should be run through --dist no, either before or after all the other tests distributed to workers.

e.g.

@pytest.mark.no_xdist
def test2(...):

My current alternative idea is to create this marker and to run 2 separate pytest command.

Start by reviewing the pytest-xdist PR #229 and the issue's proposed no_xdist marker and two-command alternative. Define how marked tests should be selected and ordered relative to distributed tests, then verify that the requested behavior works for tests that spawn and resolve network resources.