Add `TestCase.assertLogs()` backport for Python 2.7

2 files changed, 125 insertions, 1 deletions

diff --git a/certbot-nginx/tests/test_log_util.py b/certbot-nginx/tests/test_log_util.py
new file mode 100644
index 000000000..f8135ca26
--- /dev/null
+++ b/certbot-nginx/tests/test_log_util.py
@@ -0,0 +1,123 @@
+"""Backport for `TestCase.assertLogs()`.
+
+Most of the idea and code are from CPython implementation.
+https://github.com/python/cpython/blob/b76518d43fb82ed9e5d27025d18c90a23d525c90/Lib/unittest/case.py
+"""
+import logging
+import collections
+
+__all__ = ['AssertLogsMixin']
+
+LoggingWatcher = collections.namedtuple('LoggingWatcher', ['records', 'output'])
+
+
+class CapturingHandler(logging.Handler):
+    """
+    A logging handler capturing all (raw and formatted) logging output.
+    """
+
+    def __init__(self):
+        super(CapturingHandler, self).__init__()
+        self.watcher = LoggingWatcher([], [])
+
+    def flush(self):
+        pass
+
+    def emit(self, record):
+        self.watcher.records.append(record)
+        self.watcher.output.append(self.format(record))
+
+
+
+class AssertLogsContext(object):
+    """
+    A context manager used to implement `TestCase.assertLogs()`.
+    """
+
+    LOGGING_FORMAT = '%(levelname)s:%(name)s:%(message)s'
+
+    def __init__(self, test_case, logger_name, level):
+        self.test_case = test_case
+
+        self.logger_name = logger_name
+        self.logger_states = None
+        self.logger = None
+
+        if level:
+            # pylint: disable=protected-access,no-member
+            try:
+                name_to_level = logging._nameToLevel  # type: ignore
+            except AttributeError:
+                name_to_level = logging._levelNames  # type: ignore
+
+            self.level = name_to_level.get(level, level)
+        else:
+            self.level = logging.INFO
+
+        self.watcher = None
+
+    def _save_logger_states(self):
+        self.logger_states = (self.logger.handlers[:], self.logger.level, self.logger.propagate)
+
+    def _restore_logger_states(self):
+        self.logger.handlers, self.logger.level, self.logger.propagate = self.logger_states
+
+    def __enter__(self):
+        if isinstance(self.logger_name, logging.Logger):
+            self.logger = self.logger_name
+        else:
+            self.logger = logging.getLogger(self.logger_name)
+
+        formatter = logging.Formatter(self.LOGGING_FORMAT)
+
+        handler = CapturingHandler()
+        handler.setFormatter(formatter)
+
+        self._save_logger_states()
+        self.logger.handlers = [handler]
+        self.logger.setLevel(self.level)
+        self.logger.propagate = False
+
+        self.watcher = handler.watcher
+        return handler.watcher
+
+    def __exit__(self, exc_type, exc_value, tb):
+        self._restore_logger_states()
+
+        if exc_type is not None:
+            # let unexpected exceptions pass through
+            return
+
+        if not self.watcher.records:
+            self._raiseFailure(
+                "no logs of level {} or higher triggered on {}"
+                .format(logging.getLevelName(self.level), self.logger.name))
+
+    def _raiseFailure(self, message):
+        message = self.test_case._formatMessage(None, message)  # pylint: disable=protected-access
+        raise self.test_case.failureException(message)
+
+
+class AssertLogsMixin(object):
+    """
+    A mixin that implements `TestCase.assertLogs()`.
+    """
+
+    def assertLogs(self, logger=None, level=None):
+        """Fail unless a log message of level *level* or higher is emitted
+        on *logger_name* or its children.  If omitted, *level* defaults to
+        INFO and *logger* defaults to the root logger.
+        This method must be used as a context manager, and will yield
+        a recording object with two attributes: `output` and `records`.
+        At the end of the context manager, the `output` attribute will
+        be a list of the matching formatted log messages and the
+        `records` attribute will be a list of the corresponding LogRecord
+        objects.
+        Example::
+            with self.assertLogs('foo', level='INFO') as cm:
+                logging.getLogger('foo').info('first message')
+                logging.getLogger('foo.bar').error('second message')
+            self.assertEqual(cm.output, ['INFO:foo:first message',
+                                         'ERROR:foo.bar:second message'])
+        """
+        return AssertLogsContext(self, logger, level)
diff --git a/certbot-nginx/tests/test_util.py b/certbot-nginx/tests/test_util.py
index 8dfd18637..4c9da84bd 100644
--- a/certbot-nginx/tests/test_util.py
+++ b/certbot-nginx/tests/test_util.py
@@ -14,9 +14,10 @@ from certbot.plugins import common
 from certbot.tests import util as test_util
 from certbot_nginx._internal import configurator
 from certbot_nginx._internal import nginxparser
+import test_log_util
 
 
-class NginxTest(test_util.ConfigTestCase):
+class NginxTest(test_log_util.AssertLogsMixin, test_util.ConfigTestCase):
 
     def setUp(self):
         super(NginxTest, self).setUp()