Harrison/llm saving (#331)

Co-authored-by: Akash Samant <70665700+asamant21@users.noreply.github.com>

tests/unit_tests/chains/test_natbot.py

@@ -2,11 +2,13 @@
 
 from typing import Any, List, Mapping, Optional
 
+from pydantic import BaseModel
+
 from langchain.chains.natbot.base import NatBotChain
 from langchain.llms.base import LLM
 
 
-class FakeLLM(LLM):
+class FakeLLM(LLM, BaseModel):
     """Fake LLM wrapper for testing purposes."""
 
     def __call__(self, prompt: str, stop: Optional[List[str]] = None) -> str:
@@ -16,6 +18,11 @@ class FakeLLM(LLM):
         else:
             return "bar"
 
+    @property
+    def _llm_type(self) -> str:
+        """Return type of llm."""
+        return "fake"
+
     @property
     def _identifying_params(self) -> Mapping[str, Any]:
         return {}