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test_fallback_on_primary_failure() — langchain Function Reference

Architecture documentation for the test_fallback_on_primary_failure() function in test_model_fallback.py from the langchain codebase.

Function python LangChainCore LanguageModelBase calls 2

Entity Profile

Dependency Diagram

graph TD
  71674a0f_e9f0_690f_b0ff_2fdd6d3e29c2["test_fallback_on_primary_failure()"]
  c6372e75_e4e3_ed20_8230_4be219762f0f["test_model_fallback.py"]
  71674a0f_e9f0_690f_b0ff_2fdd6d3e29c2 -->|defined in| c6372e75_e4e3_ed20_8230_4be219762f0f
  87e5ea8c_f6ab_eab3_8968_7c2261cefbeb["_make_request()"]
  71674a0f_e9f0_690f_b0ff_2fdd6d3e29c2 -->|calls| 87e5ea8c_f6ab_eab3_8968_7c2261cefbeb
  fc62f046_017a_e638_7bb9_4717283b8bd6["_generate()"]
  71674a0f_e9f0_690f_b0ff_2fdd6d3e29c2 -->|calls| fc62f046_017a_e638_7bb9_4717283b8bd6
  style 71674a0f_e9f0_690f_b0ff_2fdd6d3e29c2 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_model_fallback.py lines 65–94

def test_fallback_on_primary_failure() -> None:
    """Test that fallback model is used when primary fails."""

    class FailingPrimaryModel(GenericFakeChatModel):
        @override
        def _generate(
            self,
            messages: list[BaseMessage],
            stop: list[str] | None = None,
            run_manager: CallbackManagerForLLMRun | None = None,
            **kwargs: Any,
        ) -> ChatResult:
            msg = "Primary model failed"
            raise ValueError(msg)

    primary_model = FailingPrimaryModel(messages=iter([AIMessage(content="should not see")]))
    fallback_model = GenericFakeChatModel(messages=iter([AIMessage(content="fallback response")]))

    middleware = ModelFallbackMiddleware(fallback_model)
    request = _make_request()
    request = request.override(model=primary_model)

    def mock_handler(req: ModelRequest) -> ModelResponse:
        result = req.model.invoke([])
        return ModelResponse(result=[result])

    response = middleware.wrap_model_call(request, mock_handler)

    assert isinstance(response, ModelResponse)
    assert response.result[0].content == "fallback response"

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Defined In

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Source

Frequently Asked Questions

What does test_fallback_on_primary_failure() do?
test_fallback_on_primary_failure() is a function in the langchain codebase, defined in libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_model_fallback.py.
Where is test_fallback_on_primary_failure() defined?
test_fallback_on_primary_failure() is defined in libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_model_fallback.py at line 65.
What does test_fallback_on_primary_failure() call?
test_fallback_on_primary_failure() calls 2 function(s): _generate, _make_request.

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