Ensure that fetching a logger doesn't reset its loglevel to default (#5222)

## What type of PR is this? (check all applicable)

- [ ] Refactor
- [ ] Feature
- [x] Bug Fix
- [ ] Optimization
- [ ] Documentation Update
- [ ] Community Node Submission


## Have you discussed this change with the InvokeAI team?
- [ ] Yes
- [X] No, because: minor bug

      
## Have you updated all relevant documentation?
- [X] Yes
- [ ] No


## Description

While writing regression tests for the queued downloader I discovered
that when using `InvokeAILogger.get_logger()` to fetch a
previously-created logger it resets that logger's log level to the
default specified in the global config. In other words, this didn't work
as expected:

```
import logging
from invokeai.backend.util.logging import InvokeAILogger
logger1 = InvokeAILogger.get_logger('TestLogger')
logger1.setLevel(logging.DEBUG)
logger2 = InvokeAILogger.get_logger('TestLogger')
assert logger1.level == logging.DEBUG
assert logger2.level == logging.DEBUG
```

This PR fixes the problem and adds a corresponding pytest.

## Related Tickets & Documents

<!--
For pull requests that relate or close an issue, please include them
below. 

For example having the text: "closes #1234" would connect the current
pull
request to issue 1234.  And when we merge the pull request, Github will
automatically close the issue.
-->

- Related Issue #
- Closes #

## QA Instructions, Screenshots, Recordings

<!-- 
Please provide steps on how to test changes, any hardware or 
software specifications as well as any other pertinent information. 
-->

## Added/updated tests?

- [X] Yes
- [ ] No

## [optional] Are there any post deployment tasks we need to perform?

invokeai/app/api/routers/model_records.py

@@ -141,7 +141,7 @@ async def del_model_record(
     status_code=201,
 )
 async def add_model_record(
-    config: Annotated[AnyModelConfig, Body(description="Model config", discriminator="type")]
+    config: Annotated[AnyModelConfig, Body(description="Model config", discriminator="type")],
 ) -> AnyModelConfig:
     """
     Add a model using the configuration information appropriate for its type.

invokeai/backend/util/logging.py

@@ -342,9 +342,8 @@ class InvokeAILogger(object):  # noqa D102
         cls, name: str = "InvokeAI", config: InvokeAIAppConfig = InvokeAIAppConfig.get_config()
     ) -> logging.Logger:  # noqa D102
         if name in cls.loggers:
-            logger = cls.loggers[name]
-            logger.handlers.clear()
-        else:
+            return cls.loggers[name]
+
         logger = logging.getLogger(name)
         logger.setLevel(config.log_level.upper())  # yes, strings work here
         for ch in cls.get_loggers(config):
@@ -358,7 +357,7 @@ class InvokeAILogger(object):  # noqa D102
         handlers = []
         for handler in handler_strs:
             handler_name, *args = handler.split("=", 2)
-            args = args[0] if len(args) > 0 else None
+            arg = args[0] if len(args) > 0 else None
 
             # console and file get the fancy formatter.
             # syslog gets a simple one
@@ -370,16 +369,16 @@ class InvokeAILogger(object):  # noqa D102
                 handlers.append(ch)
 
             elif handler_name == "syslog":
-                ch = cls._parse_syslog_args(args)
+                ch = cls._parse_syslog_args(arg)
                 handlers.append(ch)
 
             elif handler_name == "file":
-                ch = cls._parse_file_args(args)
+                ch = cls._parse_file_args(arg)
                 ch.setFormatter(formatter())
                 handlers.append(ch)
 
             elif handler_name == "http":
-                ch = cls._parse_http_args(args)
+                ch = cls._parse_http_args(arg)
                 handlers.append(ch)
         return handlers
 

tests/backend/util/test_logging.py

@@ -0,0 +1,57 @@
+"""
+Test interaction of logging with configuration system.
+"""
+import io
+import logging
+import re
+
+from invokeai.app.services.config import InvokeAIAppConfig
+from invokeai.backend.util.logging import LOG_FORMATTERS, InvokeAILogger
+
+
+# test formatting
+# Would prefer to use the capfd/capsys fixture here, but it is broken
+# when used with the logging module: https://github.com/pytest-dev/pytest/issue
+def test_formatting():
+    logger = InvokeAILogger.get_logger()
+    stream = io.StringIO()
+    handler = logging.StreamHandler(stream)
+    handler.setFormatter(LOG_FORMATTERS["plain"]())
+    logger.addHandler(handler)
+    logger.info("test1")
+    output = stream.getvalue()
+    assert re.search(r"\[InvokeAI\]::INFO --> test1$", output)
+
+    handler.setFormatter(LOG_FORMATTERS["legacy"]())
+    logger.info("test2")
+    output = stream.getvalue()
+    assert re.search(r">> test2$", output)
+
+
+# test independence of two loggers with different names
+def test_independence():
+    logger1 = InvokeAILogger.get_logger()
+    logger2 = InvokeAILogger.get_logger("Test")
+    assert logger1.name == "InvokeAI"
+    assert logger2.name == "Test"
+    assert logger1.level == logging.INFO
+    assert logger2.level == logging.INFO
+    logger2.setLevel(logging.DEBUG)
+    assert logger1.level == logging.INFO
+    assert logger2.level == logging.DEBUG
+
+
+# test that the logger is returned from two similar get_logger() calls
+def test_retrieval():
+    logger1 = InvokeAILogger.get_logger()
+    logger2 = InvokeAILogger.get_logger()
+    logger3 = InvokeAILogger.get_logger("Test")
+    assert logger1 == logger2
+    assert logger1 != logger3
+
+
+# test that the configuration is used to set the initial logging level
+def test_config():
+    config = InvokeAIAppConfig(log_level="debug")
+    logger1 = InvokeAILogger.get_logger("DebugTest", config=config)
+    assert logger1.level == logging.DEBUG