Avoid propagating logs (#1042)

* Avoid propagating logs

* Set up caplog for non-root loggers

* Update tests

src/fastmcp/utilities/logging.py

@@ -50,3 +50,6 @@ def configure_logging(
         logger.removeHandler(hdlr)
 
     logger.addHandler(handler)
+
+    # Don't propagate to the root logger
+    logger.propagate = False

src/fastmcp/utilities/tests.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import copy
+import logging
 import multiprocessing
 import socket
 import time
@@ -129,3 +130,15 @@ def run_server_in_process(
         proc.join(timeout=2)
         if proc.is_alive():
             raise RuntimeError("Server process failed to terminate even after kill")
+
+
+@contextmanager
+def caplog_for_fastmcp(caplog):
+    """Context manager to capture logs from FastMCP loggers even when propagation is disabled."""
+    caplog.clear()
+    logger = logging.getLogger("FastMCP")
+    logger.addHandler(caplog.handler)
+    try:
+        yield
+    finally:
+        logger.removeHandler(caplog.handler)

tests/deprecated/test_settings.py

@@ -6,6 +6,7 @@ import pytest
 
 from fastmcp import FastMCP
 from fastmcp.settings import Settings
+from fastmcp.utilities.tests import caplog_for_fastmcp
 
 # reset deprecation warnings for this module
 pytestmark = pytest.mark.filterwarnings("default::DeprecationWarning")
@@ -313,7 +314,8 @@ class TestDeprecatedEnvironmentVariables:
         try:
             os.environ[env_var_name] = "192.168.1.1"
 
-            settings = Settings()
+            with caplog_for_fastmcp(caplog):
+                settings = Settings()
 
             # Check that a warning was logged
             assert any(
@@ -341,8 +343,9 @@ class TestDeprecatedSettingsProperty:
         """Test that accessing fastmcp.settings.settings logs a deprecation warning."""
         from fastmcp import settings
 
-        # Access the deprecated property
-        deprecated_settings = settings.settings
+        with caplog_for_fastmcp(caplog):
+            # Access the deprecated property
+            deprecated_settings = settings.settings
 
         # Check that a warning was logged
         assert any(

tests/prompts/test_prompt_manager.py

@@ -7,6 +7,7 @@ from fastmcp.exceptions import NotFoundError, PromptError
 from fastmcp.prompts import Prompt
 from fastmcp.prompts.prompt import FunctionPrompt, PromptMessage, TextContent
 from fastmcp.prompts.prompt_manager import PromptManager
+from fastmcp.utilities.tests import caplog_for_fastmcp
 
 
 class TestPromptManager:
@@ -31,7 +32,10 @@ class TestPromptManager:
         manager = PromptManager(duplicate_behavior="warn")
         prompt = Prompt.from_function(fn)
         first = manager.add_prompt(prompt)
-        second = manager.add_prompt(prompt)
+
+        with caplog_for_fastmcp(caplog):
+            second = manager.add_prompt(prompt)
+
         assert first == second
         assert "Prompt already exists" in caplog.text
 
@@ -58,7 +62,9 @@ class TestPromptManager:
         prompt = Prompt.from_function(test_fn, name="test_prompt")
 
         manager.add_prompt(prompt)
-        manager.add_prompt(prompt)
+
+        with caplog_for_fastmcp(caplog):
+            manager.add_prompt(prompt)
 
         assert "Prompt already exists: test_prompt" in caplog.text
         # Should have the prompt

tests/resources/test_resource_manager.py

@@ -11,6 +11,7 @@ from fastmcp.resources import (
     ResourceTemplate,
 )
 from fastmcp.resources.resource import FunctionResource
+from fastmcp.utilities.tests import caplog_for_fastmcp
 
 
 @pytest.fixture
@@ -78,7 +79,9 @@ class TestResourceManager:
         )
 
         manager.add_resource(resource)
-        manager.add_resource(resource)
+
+        with caplog_for_fastmcp(caplog):
+            manager.add_resource(resource)
 
         assert "Resource already exists" in caplog.text
         # Should have the resource
@@ -181,7 +184,9 @@ class TestResourceManager:
         )
 
         manager.add_template(template)
-        manager.add_template(template)
+
+        with caplog_for_fastmcp(caplog):
+            manager.add_template(template)
 
         assert "Template already exists" in caplog.text
         # Should have the template

tests/server/test_mount.py

@@ -8,6 +8,7 @@ from fastmcp import FastMCP
 from fastmcp.client import Client
 from fastmcp.client.transports import FastMCPTransport, SSETransport
 from fastmcp.server.proxy import FastMCPProxy
+from fastmcp.utilities.tests import caplog_for_fastmcp
 
 
 class TestBasicMount:
@@ -290,25 +291,26 @@ class TestMultipleServerMount:
         main_app.mount(unreachable_proxy, "unreachable")
 
         # All object types should work from working server despite unreachable proxy
-        async with Client(main_app) as client:
-            # Test tools
-            tools = await client.list_tools()
-            tool_names = [tool.name for tool in tools]
-            assert "working_working_tool" in tool_names
+        with caplog_for_fastmcp(caplog):
+            async with Client(main_app) as client:
+                # Test tools
+                tools = await client.list_tools()
+                tool_names = [tool.name for tool in tools]
+                assert "working_working_tool" in tool_names
 
-            # Test calling a tool
-            result = await client.call_tool("working_working_tool", {})
-            assert result.data == "Working tool"
+                # Test calling a tool
+                result = await client.call_tool("working_working_tool", {})
+                assert result.data == "Working tool"
 
-            # Test resources
-            resources = await client.list_resources()
-            resource_uris = [str(resource.uri) for resource in resources]
-            assert "working://working/data" in resource_uris
+                # Test resources
+                resources = await client.list_resources()
+                resource_uris = [str(resource.uri) for resource in resources]
+                assert "working://working/data" in resource_uris
 
-            # Test prompts
-            prompts = await client.list_prompts()
-            prompt_names = [prompt.name for prompt in prompts]
-            assert "working_working_prompt" in prompt_names
+                # Test prompts
+                prompts = await client.list_prompts()
+                prompt_names = [prompt.name for prompt in prompts]
+                assert "working_working_prompt" in prompt_names
 
         # Verify that warnings were logged for the unreachable server
         warning_messages = [

tests/tools/test_tool.py

@@ -15,6 +15,7 @@ from typing_extensions import TypedDict
 
 from fastmcp.tools.tool import Tool, _convert_to_content
 from fastmcp.utilities.json_schema import compress_schema
+from fastmcp.utilities.tests import caplog_for_fastmcp
 from fastmcp.utilities.types import Audio, File, Image
 
 
@@ -1007,12 +1008,11 @@ class TestConvertResultToContent:
 
     def test_custom_serializer_error_fallback(self, caplog):
         """Test that if a custom serializer fails, it falls back to the default."""
-        import logging
 
         def custom_serializer_that_fails(data):
             raise ValueError("Serialization failed")
 
-        with caplog.at_level(logging.WARNING):
+        with caplog_for_fastmcp(caplog):
             result = _convert_to_content(
                 {"a": 1}, serializer=custom_serializer_that_fails
             )

tests/tools/test_tool_manager.py

@@ -12,6 +12,7 @@ from fastmcp import Context, FastMCP
 from fastmcp.exceptions import NotFoundError, ToolError
 from fastmcp.tools import FunctionTool, ToolManager
 from fastmcp.tools.tool import Tool
+from fastmcp.utilities.tests import caplog_for_fastmcp
 from fastmcp.utilities.types import Image
 
 
@@ -178,8 +179,10 @@ class TestAddTools:
 
         tool1 = Tool.from_function(test_fn, name="test_tool")
         manager.add_tool(tool1)
-        tool2 = Tool.from_function(test_fn, name="test_tool")
-        manager.add_tool(tool2)
+
+        with caplog_for_fastmcp(caplog):
+            tool2 = Tool.from_function(test_fn, name="test_tool")
+            manager.add_tool(tool2)
 
         assert "Tool already exists: test_tool" in caplog.text
         # Should have the tool