Merge user contribution from #43 (#44)

* test_logger setup: allow kwargs to be forwarded to CumulusLogger constructor

* add failing test, each logger should only have one handler

* CumulusLogger: only create new handler if one is not present

This fixes the test added in the previous commit

Before this change, multiple calls to `CumulusLogger(name)` would construct a
`CumulusLogger` instance with the same underlying `Logger` instance, but each
construction would also create and attach a new handler, resulting in duplicate
messages, e.g.:

```
> python
>>> from cumulus_logger import CumulusLogger
>>> logger = CumulusLogger('test')
>>> logger.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:18:09.315309", "level": "info"}
>>>
>>> logger2 = CumulusLogger('test')
>>> logger2.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:18:16.845070", "level": "info"}
{"message": "hello there", "timestamp": "2021-12-21T16:18:16.845070", "level": "info"}
>>>
>>> logger.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:18:18.165564", "level": "info"}
{"message": "hello there", "timestamp": "2021-12-21T16:18:18.165564", "level": "info"}
```

See also the screenshots on
ghrcdaac/dmrpp-file-generator-docker#25

With this change, a new handler is only constructed if the underlying `Logger`
does not already have any handlers, preventing messages from being handled more
than once:

```
> python
>>> from cumulus_logger import CumulusLogger
>>> logger  = CumulusLogger('test')
>>> logger.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:33:56.735453", "level": "info"}
>>>
>>> logger2 = CumulusLogger('test')
>>> logger2.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:34:03.887972", "level": "info"}
>>>
>>> logger.info('hello there')
{"message": "hello there", "timestamp": "2021-12-21T16:34:07.808415", "level": "info"}
```

Co-authored-by: Michael Brandt <michaelbrandt5@gmail.com>

cumulus_logger.py

@@ -88,15 +88,18 @@ def _get_exception_message(**kwargs):
 class CumulusLogger:
     def __init__(self, name=__name__, level=logging.DEBUG):
         """Creates a logger with a name and loggging level."""
-        log_handler = logging.StreamHandler()
-        log_handler.setLevel(logging.DEBUG)
-        log_handler.setFormatter(logging.Formatter('%(message)s'))
 
         self.logger = logging.getLogger(name)
-        self.logger.addHandler(log_handler)
         self.logger.setLevel(level)
+
         # Avoid duplicate message in AWS cloudwatch
         self.logger.propagate = False
+        if not self.logger.handlers:
+            log_handler = logging.StreamHandler()
+            log_handler.setLevel(logging.DEBUG)
+            log_handler.setFormatter(logging.Formatter('%(message)s'))
+            self.logger.addHandler(log_handler)
+
         self.event = None
         self.context = None
         self._msg = {}

tests/test_logger.py

@@ -7,15 +7,15 @@
 
 
 class TestLogger(unittest.TestCase):
-    def set_up_logger(self, event=None, context=None, logger=None):
+    def set_up_logger(self, event=None, context=None, logger=None, **kwargs):
         if event is None:
             event = create_event()
 
         if context is None:
             context = LambdaContextMock()
 
         if logger is None:
-            logger = CumulusLogger()
+            logger = CumulusLogger(**kwargs)
         logger.setMetadata(event, context)
 
         return logger
@@ -143,3 +143,11 @@ def test_message_with_json_no_kwargs(self):
         logger = self.set_up_logger()
         msg = logger.createMessage('some message about JSON and the json: {"test": "simple"}')
         self.assertEqual(msg["message"], 'some message about JSON and the json: {"test": "simple"}')
+
+    def test_multiple_instances_with_same_name_dont_have_multiple_handlers(self):
+        logger1 = self.set_up_logger(name='test')
+        self.assertEqual(1, len(logger1.logger.handlers))
+
+        logger2 = self.set_up_logger(name='test')
+        self.assertEqual(1, len(logger1.logger.handlers))
+        self.assertEqual(1, len(logger2.logger.handlers))