test_middleware_type_errors.py — langchain Source File

Source Code

"""Demonstrate type errors that mypy catches for ContextT and ResponseT mismatches.

This file contains intentional type errors to demonstrate that mypy catches them.
Run: uv run --group typing mypy <this file>

Expected errors:
1. TypedDict "UserContext" has no key "session_id" - accessing wrong context field
2. Argument incompatible with supertype - mismatched ModelRequest type
3. Cannot infer value of type parameter - middleware/context_schema mismatch
4. "AnalysisResult" has no attribute "summary" - accessing wrong response field
5. Handler returns wrong ResponseT type
"""

from __future__ import annotations

from typing import TYPE_CHECKING, Any

from pydantic import BaseModel
from typing_extensions import TypedDict

from langchain.agents import create_agent
from langchain.agents.middleware.types import (
    AgentMiddleware,
    AgentState,
    ContextT,
    ModelRequest,
    ModelResponse,
)
from tests.unit_tests.agents.model import FakeToolCallingModel

if TYPE_CHECKING:
    from collections.abc import Callable


# =============================================================================
# Context and Response schemas
# =============================================================================
class UserContext(TypedDict):
    user_id: str
    user_name: str


class SessionContext(TypedDict):
    session_id: str
    expires_at: int


class AnalysisResult(BaseModel):
    sentiment: str
    confidence: float


class SummaryResult(BaseModel):
    summary: str
    key_points: list[str]


# =============================================================================
# ERROR 1: Using wrong context fields
# =============================================================================
// ... (142 more lines)