test_todo_middleware_custom_system_prompt_in_agent() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_todo.py lines 416–439

def test_todo_middleware_custom_system_prompt_in_agent() -> None:
    """Test that custom tool executes correctly in an agent."""
    middleware = TodoListMiddleware(system_prompt="call the write_todos tool")

    model = FakeToolCallingModel(
        tool_calls=[
            [
                {
                    "args": {"todos": [{"content": "Custom task", "status": "pending"}]},
                    "name": "write_todos",
                    "type": "tool_call",
                    "id": "test_call",
                }
            ],
            [],
        ]
    )

    agent = create_agent(model=model, middleware=[middleware])

    result = agent.invoke({"messages": [HumanMessage("Hello")]})
    assert result["todos"] == [{"content": "Custom task", "status": "pending"}]
    # assert custom system prompt is in the first AI message
    assert "call the write_todos tool" in result["messages"][1].content