test_invoke_with_model_override() — langchain Function Reference

Source Code

libs/standard-tests/langchain_tests/integration_tests/chat_models.py lines 910–950

    def test_invoke_with_model_override(self, model: BaseChatModel) -> None:
        """Test that model name can be overridden at invoke time via kwargs.

        This enables dynamic model selection without creating new instances,
        which is useful for fallback strategies, A/B testing, or cost optimization.

        Test is skipped if `supports_model_override` is `False`.

        ??? question "Troubleshooting"

            If this test fails, ensure that your `_generate` method passes
            `**kwargs` through to the API request payload in a way that allows
            the `model` parameter to be overridden.

            For example:
            ```python
            def _get_request_payload(self, ..., **kwargs) -> dict:
                return {
                    "model": self.model,
                    ...
                    **kwargs,  # kwargs should come last to allow overrides
                }
            ```
        """
        if not self.supports_model_override:
            pytest.skip("Model override not supported.")

        override_model = self.model_override_value
        if not override_model:
            pytest.skip("model_override_value not specified.")

        result = model.invoke("Hello", model=override_model)
        assert result is not None
        assert isinstance(result, AIMessage)

        # Verify the overridden model was used
        model_name = result.response_metadata.get("model_name")
        assert model_name is not None, "model_name not found in response_metadata"
        assert override_model in model_name, (
            f"Expected model '{override_model}' but got '{model_name}'"
        )