Test MCP Tools

The current Python SDK can connect a Client directly to an MCPServer object, giving you fast tests without ports or subprocesses.

import pytest
from mcp.client import Client
from server import mcp

@pytest.mark.anyio
async def test_lookup():
    async with Client(mcp) as client:
        result = await client.call_tool("lookup", {"id":"A-1"})
        assert result is not None

Test more than the happy path

• Required/missing fields.
• Boundary values and enums.
• Unauthorized caller.
• Downstream timeout.
• Not-found behavior.
• Structured output contract.
• Idempotency for mutations.

Snapshot schemas selectively

Schema snapshots can catch accidental breaking changes, but make them readable and reviewable rather than snapshotting entire noisy protocol responses.