[simple] added test case and improve self class return type annotation (

langchain-ai#3773)

a simple follow up of langchain-ai#3748
- added test case
- improve annotation when function return type is class itself.

langchain/retrievers/document_compressors/chain_extract.py

@@ -1,4 +1,6 @@
 """DocumentFilter that uses an LLM chain to extract the relevant parts of documents."""
+from __future__ import annotations
+
 from typing import Any, Callable, Dict, Optional, Sequence
 
 from langchain import LLMChain, PromptTemplate
@@ -70,7 +72,7 @@ def from_llm(
         prompt: Optional[PromptTemplate] = None,
         get_input: Optional[Callable[[str, Document], str]] = None,
         llm_chain_kwargs: Optional[dict] = None,
-    ) -> "LLMChainExtractor":
+    ) -> LLMChainExtractor:
         """Initialize from LLM."""
         _prompt = prompt if prompt is not None else _get_default_chain_prompt()
         _get_input = get_input if get_input is not None else default_get_input

tests/integration_tests/retrievers/document_compressors/test_chain_extract.py

@@ -4,6 +4,14 @@
 from langchain.schema import Document
 
 
+def test_llm_construction_with_kwargs() -> None:
+    llm_chain_kwargs = {"verbose": True}
+    compressor = LLMChainExtractor.from_llm(
+        ChatOpenAI(), llm_chain_kwargs=llm_chain_kwargs
+    )
+    assert compressor.llm_chain.verbose is True
+
+
 def test_llm_chain_extractor() -> None:
     texts = [
         "The Roman Empire followed the Roman Republic.",