Prevent unwanted logging while running tests

Previously, logging messages would output to std.out. when running
individual test files (instead of running the entire suite). To
prevent this, I've added a `for`-loop to `tests.helpers` that sets
the level of all registered loggers to `CRITICAL`.

The reason for adding this to `tests.helpers` is simple: It's the
most common file to be imported in individual tests, increasing the
chance of the code being run for individual test files.

A small downside of this way of handling logging is that when we are
trying to assert logging messages are being emitted, we need to set
the logger explicitly in the `self.assertLogs` context manager. This
is a small downside, though, and probably good practice anyway.

There was one test in `tests.bot.test_api` that did not do this, so
I have changed this to make the test compatible with the new set-up.

2 files changed, 14 insertions, 1 deletions

diff --git a/tests/bot/test_api.py b/tests/bot/test_api.py
index e0ede0eb1..5a88adc5c 100644
--- a/tests/bot/test_api.py
+++ b/tests/bot/test_api.py
@@ -121,7 +121,9 @@ class LoggingHandlerTests(LoggingTestCase):
 
     def test_schedule_queued_tasks_for_nonempty_queue(self):
         """`APILoggingHandler` should schedule logs when the queue is not empty."""
-        with self.assertLogs(level=logging.DEBUG) as logs, patch('asyncio.create_task') as create_task:
+        log = logging.getLogger("bot.api")
+
+        with self.assertLogs(logger=log, level=logging.DEBUG) as logs, patch('asyncio.create_task') as create_task:
             self.log_handler.queue = [555]
             self.log_handler.schedule_queued_tasks()
             self.assertListEqual(self.log_handler.queue, [])
diff --git a/tests/helpers.py b/tests/helpers.py
index 8496ba031..8d661513d 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 import asyncio
 import functools
 import inspect
+import logging
 import unittest.mock
 from typing import Any, Iterable, Optional
 
@@ -10,6 +11,16 @@ import discord
 from discord.ext.commands import Bot, Context
 
 
+for logger in logging.Logger.manager.loggerDict.values():
+    # Set all loggers to CRITICAL by default to prevent screen clutter during testing
+
+    if not isinstance(logger, logging.Logger):
+        # There might be some logging.PlaceHolder objects in there
+        continue
+
+    logger.setLevel(logging.CRITICAL)
+
+
 def async_test(wrapped):
     """
     Run a test case via asyncio.