check testcase format if valid

def _check_format(file_path, content):
    """ check testcase format if valid
    """
    # TODO: replace with JSON schema validation
    if not content:
        # testcase file content is empty
        err_msg = u"Testcase file content is empty: {}".format(file_path)
        logger.log_error(err_msg)
        raise exceptions.FileFormatError(err_msg)

    elif not isinstance(content, (list, dict)):
        # testcase file content does not match testcase format
        err_msg = u"Testcase file content format invalid: {}".format(file_path)
        logger.log_error(err_msg)
        raise exceptions.FileFormatError(err_msg)