TestMaxToolsLimiting Class — langchain Architecture

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_selection.py lines 210–334

class TestMaxToolsLimiting:
    """Test max_tools limiting behavior."""

    def test_max_tools_limits_selection(self) -> None:
        """Test that max_tools limits selection when model selects too many tools."""
        model_requests = []

        @wrap_model_call
        def trace_model_requests(
            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
        ) -> ModelResponse:
            model_requests.append(request)
            return handler(request)

        # Selector model tries to select 4 tools
        tool_selection_model = FakeModel(
            messages=cycle(
                [
                    AIMessage(
                        content="",
                        tool_calls=[
                            {
                                "name": "ToolSelectionResponse",
                                "id": "1",
                                "args": {
                                    "tools": [
                                        "get_weather",
                                        "search_web",
                                        "calculate",
                                        "send_email",
                                    ]
                                },
                            }
                        ],
                    ),
                ]
            )
        )

        model = FakeModel(messages=iter([AIMessage(content="Done")]))

        # But max_tools=2, so only first 2 should be used
        tool_selector = LLMToolSelectorMiddleware(max_tools=2, model=tool_selection_model)

        agent = create_agent(
            model=model,
            tools=[get_weather, search_web, calculate, send_email],
            middleware=[tool_selector, trace_model_requests],
        )

        agent.invoke({"messages": [HumanMessage("test")]})

        # Verify only 2 tools were passed to the main model
        assert len(model_requests) > 0
        for request in model_requests:
            assert len(request.tools) == 2
            tool_names = []
            for tool_ in request.tools:
                assert isinstance(tool_, BaseTool)
                tool_names.append(tool_.name)
            # Should be first 2 from the selection
            assert tool_names == ["get_weather", "search_web"]

    def test_no_max_tools_uses_all_selected(self) -> None:
        """Test that when max_tools is None, all selected tools are used."""
        model_requests = []

        @wrap_model_call
        def trace_model_requests(
            request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]
        ) -> ModelResponse:
            model_requests.append(request)
            return handler(request)

        tool_selection_model = FakeModel(
            messages=cycle(
                [
                    AIMessage(
                        content="",
                        tool_calls=[
                            {