a snipped from pytest_select plugin

plugin.py

def pytest_collection_modifyitems(session, config, items):

    seen_test_names = set()
    for item in items:
        seen_test_names.add(item.name)
        seen_test_names.add(item.nodeid)

    selection_file_name = config.getoption("deselectfromfile")
    if selection_file_name is not None:

        selection_file_path = Path(selection_file_name)
        with selection_file_path.open("rt", encoding="UTF-8") as selection_file:
            test_names = {test_name.strip() for test_name in selection_file}


    missing_test_names = test_names - seen_test_names
    if missing_test_names:
        # If any items remain in `test_names` those tests either don't exist or
        # have been deselected by another way - warn user

        message = (
            f"pytest-select: Missing deselected test names:\n - "
        )
        message += "\n  - ".join(missing_test_names)
        if config.getoption("selectfailonmissing"):
            raise UsageError(message)
        warnings.warn(message, PytestSelectWarning)

    for item in items:
        if item.name in test_names or item.nodeid in test_names:
            item.add_marker(skip)