Fix flaky test test_response in test_streamable_http.py

[maxisbey]

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

The test is flaky. See: https://github.com/modelcontextprotocol/python-sdk/actions/runs/19020904095/job/54315849330?pr=1565

Output:

basic_server = None, basic_server_url = 'http://127.0.0.1:50695/'

    def test_response(basic_server: None, basic_server_url: str):
        """Test response handling for a valid request."""
        mcp_url = f"{basic_server_url}/mcp"
        response = requests.post(
            mcp_url,
            headers={
                "Accept": "application/json, text/event-stream",
                "Content-Type": "application/json",
            },
            json=INIT_REQUEST,
        )
>       assert response.status_code == 200
E       assert 404 == 200
E        +  where 404 = <Response [404]>.status_code

tests/shared/test_streamable_http.py:624: AssertionError

Example Code

Python & MCP Python SDK

1.19.0