def display_warnings(_warnings):
    """
    Return a string that displays a list of unexpected warnings

    Parameters
    ----------
    _warnings : iterable
        List of warnings to be displayed

    Returns
    -------
    msg : str
        String containing the warning messages to be displayed
    """
    if len(_warnings) == 0:
        return "No warnings occurred (was one expected?)"

    msg = "Unexpected warning(s) occurred:\n"
    for warning in _warnings:
        msg += "{}:{}: {}: {}\n".format(
            warning.filename,
            warning.lineno,
            warning.category.__name__,
            warning.message)
    return msg