Answering Jeff's question from https://alysivji.github.io/pytest-fixures-with-function-arguments.html

test_interface_pytest.py

import pytest

import interface

@pytest.fixture(scope='session')
def run_command_mock(mocker):
    def _create_run_command_mock(mock_return_value):
        mock_run = mocker.MagicMock(name='run command mock')
        mock_run.return_value = "foo"
        run_command_patch = mocker.patch('interface.run_command', new=mock_run)
        return run_command_patch
    
    return _create_run_command_mock

@jeffsilverm mocker is a pytest fixture https://github.com/pytest-dev/pytest-mock