test_state_passthrough() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_framework.py lines 916–928

    def test_state_passthrough(self) -> None:
        """Test that state modifications in before_agent are visible to after_agent."""

        @before_agent
        def modify_in_before(*_args: Any, **_kwargs: Any) -> dict[str, Any]:
            return {"messages": [HumanMessage("Added by before_agent")]}

        model = GenericFakeChatModel(messages=iter([AIMessage(content="Response")]))
        agent = create_agent(model=model, tools=[], middleware=[modify_in_before])
        result = agent.invoke({"messages": [HumanMessage("Original")]})

        message_contents = [msg.content for msg in result["messages"]]
        assert message_contents[1] == "Added by before_agent"