Python 3 单元测试 - 未调用断言记录器

Question

我知道如何断言已生成日志消息，但我似乎无法弄清楚如何断言未生成日志消息。这是我现在的单元测试(已清理)。请注意，XYZ 类将记录器作为参数，而 test_check_unexpected_keys_found 按预期通过。

import unittest
import logging

class TestXYZ(unittest.TestCase):

    @classmethod
    def setUpClass(cls):
        cls.test_logger = logging.getLogger('test_logger')
        cls.test_logger.addHandler(logging.NullHandler())

    def test_check_unexpected_keys_found(self):
        test_dict = {
            'unexpected': 0,
            'expected1': 1,
            'expected2': 2,
        }
        xyz = XYZ(self.test_logger)
        with self.assertLogs('test_logger', level='WARNING'):
            xyz._check_unexpected_keys(test_dict)

    def test_check_unexpected_keys_none(self):
        test_dict = {
            'expected1': 1,
            'expected2': 2,
        }
        xyz = XYZ(self.test_logger)
        xyz._check_unexpected_keys(test_dict)
        # assert that 'test_logger' was not called ??

我尝试使用 unittest.patch 像这样:

with patch('TestXYZ.test_logger.warning') as mock_logwarn:
    xyz._check_unexpected_keys(test_dict)
    self.assertFalse(mock_logwarn.called)

但我收到 ImportError: No module named 'TestXYZ'
我也尝试了一些变体，但一无所获。

有谁知道如何处理这个？

Answer 1

全新 assertNoLogs方法是 on route to be added to a future version of Python .
在此之前，这里有一个解决方法:添加一个虚拟日志，然后断言它是唯一的日志。

with self.assertLogs(logger, logging.WARN) as cm:
    # We want to assert there are no warnings, but the 'assertLogs' method does not support that.
    # Therefore, we are adding a dummy warning, and then we will assert it is the only warning.
    logger.warn("Dummy warning")
    # DO STUFF

self.assertEqual(
    ["Dummy warning"],
    cm.output,
)

如果您需要这样做不止一次，那么为了避免重复，您可以执行以下操作。假设您有一个所有测试类都继承自的基类，覆盖 assertLogs在该类中如下:

class TestBase(TestCase):
    def assertLogs(self, logger_to_watch=None, level=None) -> 'CustomAssertLogsContext':
        """
        This method overrides the one in `unittest.case.TestCase`, and has the same behavior, except for not causing a failure when there are no log messages.
        The point is to allow asserting there are no logs.
        Get rid of this once this is resolved: https://github.com/python/cpython/pull/18067
        """
        return CustomAssertLogsContext(self, logger_to_watch, level)

class CustomAssertLogsContext(_AssertLogsContext):    
    def __exit__(self, exc_type, exc_val, exc_tb) -> Optional[bool]:
        # Fool the original exit method to think there is at least one record, to avoid causing a failure
        self.watcher.records.append("DUMMY")
        result = super().__exit__(exc_type, exc_val, exc_tb)
        self.watcher.records.pop()
        return result