def _validate_documentation_existence(moler_module, test_data, observer_type):
    """Check if module has at least one variant of output documented"""
    if len(test_data.keys()) == 0:
        expected_info = '{}_OUTPUT/{}_KWARGS/{}_RESULT'.format(observer_type,
            observer_type, observer_type)
        error_msg = '{} is missing documentation: {}'.format(moler_module,
            expected_info)
        return error_msg
    return ''
