def should_skip(core):
    """Is there a reason to skip these tests?

    Return empty string to run tests, or a message about why we are skipping
    the tests.
    """
    skipper = ""

    # $set_env.py: COVERAGE_TEST_CORES - List of cores to run
    test_cores = os.getenv("COVERAGE_TEST_CORES")
    if test_cores:
        if core not in test_cores:
            skipper = f"core {core} not in COVERAGE_TEST_CORES={test_cores}"
    else:
        # $set_env.py: COVERAGE_ONE_CORE - Only run tests for one core.
        only_one = os.getenv("COVERAGE_ONE_CORE")
        if only_one:
            if CPYTHON:
                if sys.version_info >= (3, 12):
                    if core != "sysmon":
                        skipper = f"Only one core: not running {core}"
                elif core != "ctrace":
                    skipper = f"Only one core: not running {core}"
            else:
                if core != "pytrace":
                    skipper = f"No C core for {platform.python_implementation()}"

    if skipper:
        return f"Skipping tests {label_for_core(core)}: {skipper}"
    else:
        return ""
Is there a reason to skip these tests?

    Return empty string to run tests, or a message about why we are skipping
    the tests.
    
igor.py