问题

我有一个用于删除文件的实用函数如下。
我打算为它编写单元测试用例。

    """
    删除给定的文件名
    """
    try:
        os.remove(file_name)
        logger.info("已删除文件：%s", file_name)
    except FileNotFoundError:
        logger.error("错误：找不到文件%s", file_name)
    except PermissionError:
        logger.error("删除时无效权限：%s", file_name)
    except OSError as exc:
        logger.error("删除%s时出错：%s", exc.filename, exc.strerror)

我应该如何编写测试用例？
考虑到这些异常实际上并未引发，而是通过日志消息处理。
关于断言，有何指示？

尝试下面的代码，但它显示引发了一个错误。

def test_file_delete_with_os_error(self, mock_remove):
    mock_remove.side_effect = OSError
    with self.assertRaises(OSError):
        delete_file_name('abc.txt', logging.getLogger('test'))```

<details>
<summary>英文:</summary>

I have a utility function for removing a file as below. 
And I intend to write unittest cases for it. 

def delete_file_name(file_name, logger):
"""
Deletes given file name
"""
try:
os.remove(file_name)
logger.info("Deleted file: %s", file_name)
except FileNotFoundError:
logger.error("Error: File not found %s", file_name)
except PermissionError:
logger.error("Invalid permissions while deleting: %s", file_name)
except OSError as exc:
logger.error("Error while deleting %s: %s", exc.filename, exc.strerror)

How do I go about writing test cases? 
Considering that these exceptions are not really raised but handled by a log message.
Any pointers on how the assertions would be? 

Tried below but it shows an error that exception is not raised. 

@patch('os.remove')
def test_file_delete_with_os_error(self, mock_remove):
    mock_remove.side_effect = OSError
    with self.assertRaises(OSError):
        delete_file_name('abc.txt', logging.getLogger('test'))

</details>


# 答案1
**得分**: 2

因为您控制传递给被测试函数的记录器，所以您可以将输出重定向到自定义的 `io.StringIO` 对象：

```python
import logging
import unittest
from unittest.mock import patch

# 模拟的部分，请根据您的需求进行调整
from my_module import delete_file_name

class TestSomething(unittest.TestCase):
   def setUp(self):
       self.stream = io.StringIO()
       self.logger = logging.getLogger('test')
       self.stream_handler = logging.StreamHandler(self.stream)
       self.logger.addHandler(self.stream_handler)

   def tearDown(self):
       self.logger.removeHandler(self.stream_handler)

   @patch('os.remove')
   def test_delte_file_os_error(self, mock_remove):
       mock_remove.side_effect = OSError
       delete_file_name('abc.txt', self.logger)

       self.stream.seek(0)
       self.assertEqual(self.stream.read(), 'Error while deleting None: None\n')

正如您所看到的，然后您可以检索记录器的输出并检查它是否等于您的预期结果。
（在这个示例中，我将 Error while deleting None: None 放在那里，因为这是您目前已经放置的 side_effect 所产生的输出。）

import logging
import unittest
from unittest.mock import patch

# simulated, adjust to your needs
from my_module import delete_file_name

class TestSomething(unittest.TestCase):
    def setUp(self):
        self.stream = io.StringIO()
        self.logger = logging.getLogger('test')
        self.stream_handler = logging.StreamHandler(self.stream)
        self.logger.addHandler(self.stream_handler)

    def tearDown(self):
        self.logger.removeHandler(self.stream_handler)

    @patch('os.remove')
    def test_delte_file_os_error(self, mock_remove):
        mock_remove.side_effect = OSError
        delete_file_name('abc.txt', self.logger)

        self.stream.seek(0)
        self.assertEqual(self.stream.read(), 'Error while deleting None: None\n')