mcp-python-sdk/tests/client/conftest.py

from contextlib import asynccontextmanager
from unittest.mock import patch

import pytest

import mcp.shared.memory
from mcp.shared.message import SessionMessage
from mcp.types import (
    JSONRPCNotification,
    JSONRPCRequest,
)


class SpyMemoryObjectSendStream:
    def __init__(self, original_stream):
        self.original_stream = original_stream
        self.sent_messages: list[SessionMessage] = []

    async def send(self, message):
        self.sent_messages.append(message)
        await self.original_stream.send(message)

    async def aclose(self):
        await self.original_stream.aclose()

    async def __aenter__(self):
        return self

    async def __aexit__(self, *args):
        await self.aclose()


class StreamSpyCollection:
    def __init__(
        self,
        client_spy: SpyMemoryObjectSendStream,
        server_spy: SpyMemoryObjectSendStream,
    ):
        self.client = client_spy
        self.server = server_spy

    def clear(self) -> None:
        """Clear all captured messages."""
        self.client.sent_messages.clear()
        self.server.sent_messages.clear()

    def get_client_requests(self, method: str | None = None) -> list[JSONRPCRequest]:
        """Get client-sent requests, optionally filtered by method."""
        return [
            req.message.root
            for req in self.client.sent_messages
            if isinstance(req.message.root, JSONRPCRequest) and (method is None or req.message.root.method == method)
        ]

    def get_server_requests(self, method: str | None = None) -> list[JSONRPCRequest]:
        """Get server-sent requests, optionally filtered by method."""
        return [
            req.message.root
            for req in self.server.sent_messages
            if isinstance(req.message.root, JSONRPCRequest) and (method is None or req.message.root.method == method)
        ]

    def get_client_notifications(self, method: str | None = None) -> list[JSONRPCNotification]:
        """Get client-sent notifications, optionally filtered by method."""
        return [
            notif.message.root
            for notif in self.client.sent_messages
            if isinstance(notif.message.root, JSONRPCNotification)
            and (method is None or notif.message.root.method == method)
        ]

    def get_server_notifications(self, method: str | None = None) -> list[JSONRPCNotification]:
        """Get server-sent notifications, optionally filtered by method."""
        return [
            notif.message.root
            for notif in self.server.sent_messages
            if isinstance(notif.message.root, JSONRPCNotification)
            and (method is None or notif.message.root.method == method)
        ]


@pytest.fixture
def stream_spy():
    """Fixture that provides spies for both client and server write streams.

    Example usage:
        async def test_something(stream_spy):
            # ... set up server and client ...

            spies = stream_spy()

            # Run some operation that sends messages
            await client.some_operation()

            # Check the messages
            requests = spies.get_client_requests(method="some/method")
            assert len(requests) == 1

            # Clear for the next operation
            spies.clear()
    """
    client_spy = None
    server_spy = None

    # Store references to our spy objects
    def capture_spies(c_spy, s_spy):
        nonlocal client_spy, server_spy
        client_spy = c_spy
        server_spy = s_spy

    # Create patched version of stream creation
    original_create_streams = mcp.shared.memory.create_client_server_memory_streams

    @asynccontextmanager
    async def patched_create_streams():
        async with original_create_streams() as (client_streams, server_streams):
            client_read, client_write = client_streams
            server_read, server_write = server_streams

            # Create spy wrappers
            spy_client_write = SpyMemoryObjectSendStream(client_write)
            spy_server_write = SpyMemoryObjectSendStream(server_write)

            # Capture references for the test to use
            capture_spies(spy_client_write, spy_server_write)

            yield (client_read, spy_client_write), (server_read, spy_server_write)

    # Apply the patch for the duration of the test
    with patch("mcp.shared.memory.create_client_server_memory_streams", patched_create_streams):
        # Return a collection with helper methods
        def get_spy_collection() -> StreamSpyCollection:
            assert client_spy is not None, "client_spy was not initialized"
            assert server_spy is not None, "server_spy was not initialized"
            return StreamSpyCollection(client_spy, server_spy)

        yield get_spy_collection