fake messages list model (#10152)

create a fake chat model that you can configure with list of messages

libs/langchain/langchain/chat_models/fake.py

@@ -7,9 +7,35 @@ from langchain.callbacks.manager import (
     AsyncCallbackManagerForLLMRun,
     CallbackManagerForLLMRun,
 )
-from langchain.chat_models.base import SimpleChatModel
+from langchain.chat_models.base import BaseChatModel, SimpleChatModel
+from langchain.schema import ChatResult
 from langchain.schema.messages import AIMessageChunk, BaseMessage
-from langchain.schema.output import ChatGenerationChunk
+from langchain.schema.output import ChatGeneration, ChatGenerationChunk
+
+
+class FakeMessagesListChatModel(BaseChatModel):
+    responses: List[BaseMessage]
+    sleep: Optional[float] = None
+    i: int = 0
+
+    def _generate(
+        self,
+        messages: List[BaseMessage],
+        stop: Optional[List[str]] = None,
+        run_manager: Optional[CallbackManagerForLLMRun] = None,
+        **kwargs: Any,
+    ) -> ChatResult:
+        response = self.responses[self.i]
+        if self.i < len(self.responses) - 1:
+            self.i += 1
+        else:
+            self.i = 0
+        generation = ChatGeneration(message=response)
+        return ChatResult(generations=[generation])
+
+    @property
+    def _llm_type(self) -> str:
+        return "fake-messages-list-chat-model"
 
 
 class FakeListChatModel(SimpleChatModel):