bpo-40275: Avoid importing logging in test.support (GH-19601)

Import logging lazily in assertLogs() in unittest.
Move TestHandler from test.support to logging_helper.

1 files changed, 2 insertions, 68 deletions

diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index d0ee561..f8bc865 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -3,7 +3,6 @@
 import sys
 import functools
 import difflib
-import logging
 import pprint
 import re
 import warnings
@@ -297,73 +296,6 @@ class _AssertWarnsContext(_AssertRaisesBaseContext):
 
 
 
-_LoggingWatcher = collections.namedtuple("_LoggingWatcher",
-                                         ["records", "output"])
-
-
-class _CapturingHandler(logging.Handler):
-    """
-    A logging handler capturing all (raw and formatted) logging output.
-    """
-
-    def __init__(self):
-        logging.Handler.__init__(self)
-        self.watcher = _LoggingWatcher([], [])
-
-    def flush(self):
-        pass
-
-    def emit(self, record):
-        self.watcher.records.append(record)
-        msg = self.format(record)
-        self.watcher.output.append(msg)
-
-
-
-class _AssertLogsContext(_BaseTestCaseContext):
-    """A context manager used to implement TestCase.assertLogs()."""
-
-    LOGGING_FORMAT = "%(levelname)s:%(name)s:%(message)s"
-
-    def __init__(self, test_case, logger_name, level):
-        _BaseTestCaseContext.__init__(self, test_case)
-        self.logger_name = logger_name
-        if level:
-            self.level = logging._nameToLevel.get(level, level)
-        else:
-            self.level = logging.INFO
-        self.msg = None
-
-    def __enter__(self):
-        if isinstance(self.logger_name, logging.Logger):
-            logger = self.logger = self.logger_name
-        else:
-            logger = self.logger = logging.getLogger(self.logger_name)
-        formatter = logging.Formatter(self.LOGGING_FORMAT)
-        handler = _CapturingHandler()
-        handler.setFormatter(formatter)
-        self.watcher = handler.watcher
-        self.old_handlers = logger.handlers[:]
-        self.old_level = logger.level
-        self.old_propagate = logger.propagate
-        logger.handlers = [handler]
-        logger.setLevel(self.level)
-        logger.propagate = False
-        return handler.watcher
-
-    def __exit__(self, exc_type, exc_value, tb):
-        self.logger.handlers = self.old_handlers
-        self.logger.propagate = self.old_propagate
-        self.logger.setLevel(self.old_level)
-        if exc_type is not None:
-            # let unexpected exceptions pass through
-            return False
-        if len(self.watcher.records) == 0:
-            self._raiseFailure(
-                "no logs of level {} or higher triggered on {}"
-                .format(logging.getLevelName(self.level), self.logger.name))
-
-
 class _OrderedChainMap(collections.ChainMap):
     def __iter__(self):
         seen = set()
@@ -854,6 +786,8 @@ class TestCase(object):
             self.assertEqual(cm.output, ['INFO:foo:first message',
                                          'ERROR:foo.bar:second message'])
         """
+        # Lazy import to avoid importing logging if it is not needed.
+        from ._log import _AssertLogsContext
         return _AssertLogsContext(self, logger, level)
 
     def _getAssertEqualityFunc(self, first, second):