Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

When running the test suite on a Chinese (Simplified, zh_CN) Windows system, one of the assertions failed due to language differences.

Environment

• OS: Windows 11 (Simplified Chinese)
• Python version: 3.11

Expected Behavior

The test should pass regardless of system language.

Actual Behavior

The test fails with an AssertionError:

Suggestion

In Windows, it is modified to determine based on error codes.

assert (
    "nonexistent" in error_message
    or "not found" in error_message.lower()
    or "[winerror 2]" in error_message  # or "cannot find the file" in error_message.lower()  # Windows error message
)

Example Code

uv run pytest tests/client/test_stdio.py::test_stdio_client_nonexistent_command

Python & MCP Python SDK

Python version: 3.11
MCP Python SDK：latest