test_system_message.py — langchain Source File

Source Code

"""Comprehensive unit tests for system message handling in agents.

This module consolidates all system message and dynamic prompt tests:
- Basic system message scenarios (none, string, SystemMessage)
- ModelRequest system_message field support
- System message updates via middleware
- Multiple middleware chaining
- Cache control preservation
- Metadata merging
- Dynamic system prompt middleware
- Edge cases and error handling

These tests replicate functionality from langchainjs PR #9459.
"""

from collections.abc import Callable
from dataclasses import dataclass
from typing import Any

import pytest
from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
from langchain_core.messages import AIMessage, HumanMessage, SystemMessage, TextContentBlock
from langgraph.runtime import Runtime

from langchain.agents.factory import create_agent
from langchain.agents.middleware.types import AgentState, ModelRequest, ModelResponse


def _make_request(
    system_message: SystemMessage | None = None,
    system_prompt: str | None = None,
) -> ModelRequest:
    """Create a minimal ModelRequest for testing."""
    model = GenericFakeChatModel(messages=iter([AIMessage(content="response")]))
    return ModelRequest(
        model=model,
        system_message=system_message,
        system_prompt=system_prompt,
        messages=[],
        tool_choice=None,
        tools=[],
        response_format=None,
        state=AgentState(messages=[]),
        runtime=Runtime(),
        model_settings={},
    )


# =============================================================================
# ModelRequest Tests
# =============================================================================


class TestModelRequestSystemMessage:
    """Test ModelRequest with system_message field."""

    @pytest.mark.parametrize(
        ("system_message", "system_prompt", "expected_msg", "expected_prompt"),
        [
            # Test with SystemMessage
// ... (1004 more lines)