Fix test cleanup for uvicorn 0.39+ context isolation

[jlowin]

Uvicorn 0.39.0 introduced a fix for ContextVars pollution (encode/uvicorn#2742) that wraps ASGI tasks in empty contexts. This is a workaround for a CPython bug (python/cpython#140947) being fixed in Python 3.13+.

The context isolation breaks task cancellation propagation, causing test cleanup to hang when we task.cancel() and await task on uvicorn server tasks.

Fix: Use graceful shutdown (server.should_exit = True) for real uvicorn servers, and add timeouts for mocked server cleanup.

Files changed:

• tests/server/test_logging.py - Add timeout to mocked server cleanup
• tests/client/test_streamable_http.py - Use graceful shutdown for nested_server fixture
• tests/client/test_sse.py - Use graceful shutdown for nested_sse_server fixture

[marvin-context-protocol]

Test Failure Analysis

Summary: One test is failing: test_validation_error_propagates_from_dependency expects FastMCP's ValidationError to propagate unchanged, but it's being wrapped in a ToolError.

Root Cause: In src/fastmcp/tools/tool_manager.py:161, the code catches Pydantic's ValidationError (imported from pydantic), but not FastMCP's ValidationError (from fastmcp.exceptions). When a tool's dependency raises FastMCP's ValidationError, it propagates through the dependency system (as intended by #2633), but then gets caught by the generic Exception handler at line 167, which wraps it in a ToolError with the message "Error calling tool 'tool_with_validation': Invalid input format" instead of just "Invalid input format".

Suggested Solution: Add an exception handler for FastMCP's error types before the generic Exception handler in tool_manager.py:

# In src/fastmcp/tools/tool_manager.py, around line 161
try:
    return await tool.run(arguments)
except ValidationError as e:  # Pydantic ValidationError
    logger.exception(f"Error validating tool {key!r}: {e}")
    raise e
except ToolError as e:  # Already a ToolError
    logger.exception(f"Error calling tool {key!r}")
    raise e
except FastMCPError as e:  # Add this handler for ValidationError, ResourceError, etc.
    logger.exception(f"Error calling tool {key!r}")
    raise e
except Exception as e:  # Generic exceptions
    logger.exception(f"Error calling tool {key!r}")
    if self.mask_error_details:
        raise ToolError(f"Error calling tool {key!r}") from e
    else:
        raise ToolError(f"Error calling tool {key!r}: {e}") from e

This ensures that FastMCP's ValidationError (and other FastMCPError subclasses) propagate unchanged, as intended by the fix in commit afb22c4.

Detailed Analysis

Test Output

FAILED tests/server/test_dependencies.py::test_validation_error_propagates_from_dependency
AssertionError: assert 'Error calling tool \'tool_with_validation\': Invalid input format' == 'Invalid input format'

Code Flow

1. Test raises fastmcp.exceptions.ValidationError("Invalid input format") in a dependency
2. Dependency system correctly propagates it unchanged (per commit afb22c4)
3. ToolManager.call_tool() catches it as Exception at line 167
4. Gets wrapped in ToolError(f"Error calling tool {key!r}: {e}")
5. Test expects just "Invalid input format" but receives "Error calling tool 'tool_with_validation': Invalid input format"

Related Files

• src/fastmcp/tools/tool_manager.py:161-172 - Exception handling in call_tool()
• src/fastmcp/exceptions.py:10-11 - FastMCP's ValidationError class
• tests/server/test_dependencies.py:761-779 - Failing test
• Commit afb22c4 - Added test expecting ValidationError to propagate

Related Files

• src/fastmcp/tools/tool_manager.py:161-172 - Exception handling logic that needs to catch FastMCPError subclasses
• src/fastmcp/exceptions.py:6-19 - Defines FastMCPError base class and subclasses including ValidationError
• tests/server/test_dependencies.py:761-779 - Test that expects unchanged error propagation
• src/fastmcp/server/dependencies.py:189-194 - Dependency system that correctly propagates FastMCPError (per commit afb22c4)

---

Note: This failure is unrelated to the uvicorn context isolation fixes in this PR. The modified test files (test_sse.py, test_streamable_http.py, test_logging.py) all pass successfully.

[Kludex]

I'm reverting that PR from Uvicorn, not sure how it impacts you. But please ping me if you have any questions.