Harrison/fix and test caching (langchain-ai#538)

langchain/llms/base.py

@@ -96,7 +96,7 @@ def generate(
         new_results = self._generate(missing_prompts, stop=stop)
         self.callback_manager.on_llm_end(new_results)
         for i, result in enumerate(new_results.generations):
-            existing_prompts[i] = result
+            existing_prompts[missing_prompt_idxs[i]] = result
             prompt = prompts[i]
             langchain.llm_cache.update(prompt, llm_string, result)
         generations = [existing_prompts[i] for i in range(len(prompts))]

tests/unit_tests/llms/test_base.py

@@ -0,0 +1,27 @@
+"""Test base LLM functionality."""
+import langchain
+from langchain.cache import InMemoryCache
+from langchain.schema import Generation, LLMResult
+from tests.unit_tests.llms.fake_llm import FakeLLM
+
+
+def test_caching() -> None:
+    """Test caching behavior."""
+    langchain.llm_cache = InMemoryCache()
+    llm = FakeLLM()
+    params = llm._llm_dict()
+    params["stop"] = None
+    llm_string = str(sorted([(k, v) for k, v in params.items()]))
+    langchain.llm_cache.update("foo", llm_string, [Generation(text="fizz")])
+    output = llm.generate(["foo", "bar", "foo"])
+    langchain.llm_cache = None
+    expected_generations = [
+        [Generation(text="fizz")],
+        [Generation(text="foo")],
+        [Generation(text="fizz")],
+    ]
+    expected_output = LLMResult(
+        expected_generations,
+        llm_output=None,
+    )
+    assert output == expected_output