请问为什么我用allure生成的测试报告都是ALLURE REPORT UNKNOWN unknown - unknown (Unknown) 0 test cases NaN%?

测试代码是这样的

# -*- coding: utf-8 -*-

# @File    : test_case.py

import os
import allure
import pytest


@allure.feature('test_module_01')
def test_case_01():
    """用例描述:Test case 01"""

    assert 0 == 0


@allure.feature('test_module_02')
def test_case_02():
    """用例描述:Test case 02"""

    assert 0 == 0


if __name__ == '__main__':
    pytest.main(['-s', '-v', '--alluredir', './report'])

    os.system('allure generate ./temp -o ./report --clean')

运行之后生成了测试报告,打开报告:
图片说明

请问这是为什么呢

https://www.jianshu.com/p/b5a6e902c9d4