unittest 断言失败后控制台打印“断言失败”次数问题

[是香香本人]

我的代码：

import unittest
from ddt import ddt, data


@ddt
class TestDdt(unittest.TestCase):
    def setUp(self):
        print("setUp每个测试用例执行前都执行一次")

    def tearDown(self):
        print("tearDown每个测试用例执行后都执行一次")

    @data(1,2)
    def test_single_element(self, value):
        """
        测试单组元素
        :return:
        """
        print(value)
        self.assertEqual(value,1)


if __name__ == '__main__':
    unittest.main()

结果：

setUp每个测试用例执行前都执行一次
1
tearDown每个测试用例执行后都执行一次
setUp每个测试用例执行前都执行一次
2
tearDown每个测试用例执行后都执行一次


1 != 2

期望:2
实际 :1
<点击查看差异>

Traceback (most recent call last):
  File "F:\PyCharm\PyCharm Community Edition 2020.2\plugins\python-ce\helpers\pycharm\teamcity\diff_tools.py", line 32, in _patched_equals
    old(self, first, second, msg)
  File "C:\Users\ljx\AppData\Local\Programs\Python\Python38\lib\unittest\case.py", line 912, in assertEqual
    assertion_func(first, second, msg=msg)
  File "C:\Users\ljx\AppData\Local\Programs\Python\Python38\lib\unittest\case.py", line 905, in _baseAssertEqual
    raise self.failureException(msg)
AssertionError: 2 != 1

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\ljx\AppData\Local\Programs\Python\Python38\lib\unittest\case.py", line 60, in testPartExecutor
    yield
  File "C:\Users\ljx\AppData\Local\Programs\Python\Python38\lib\unittest\case.py", line 676, in run
    self._callTestMethod(testMethod)
  File "C:\Users\ljx\AppData\Local\Programs\Python\Python38\lib\unittest\case.py", line 633, in _callTestMethod
    method()
  File "E:\pythonProject_1\venv\lib\site-packages\ddt.py", line 182, in wrapper
    return func(self, *args, **kwargs)
  File "E:\pythonProject_1\Excel_operation\for_ddt.py", line 20, in test_single_element
    self.assertEqual(value,1)



Ran 2 tests in 0.006s

FAILED (failures=1)

进程已结束，退出代码 1

断言失败

断言失败

断言失败

这里断言成功一次，失败一次，但是为什么打印了3次断言失败呢？