langchain/llms/fake.py/FakeListLLM/_call
class FakeListLLM:    def _call(
        self,
        prompt: str,
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
    ) -> str:
        """First try to lookup in queries, else return 'foo' or 'bar'."""
        response = self.responses[self.i]
        self.i += 1
        return response