BUGFIX: anthropic models on bedrock (#13629)

Introduced in #13403

libs/langchain/tests/unit_tests/chat_models/test_bedrock.py

@@ -1,8 +1,10 @@
 """Test Anthropic Chat API wrapper."""
 from typing import List
+from unittest.mock import MagicMock
 
 import pytest
 
+from langchain.chat_models import BedrockChat
 from langchain.chat_models.meta import convert_messages_to_prompt_llama
 from langchain.schema import AIMessage, BaseMessage, HumanMessage, SystemMessage
 
@@ -28,3 +30,19 @@ from langchain.schema import AIMessage, BaseMessage, HumanMessage, SystemMessage
 def test_formatting(messages: List[BaseMessage], expected: str) -> None:
     result = convert_messages_to_prompt_llama(messages)
     assert result == expected
+
+
+def test_anthropic_bedrock() -> None:
+    client = MagicMock()
+    respbody = MagicMock(
+        read=MagicMock(
+            return_value=MagicMock(
+                decode=MagicMock(return_value=b'{"completion":"Hi back"}')
+            )
+        )
+    )
+    client.invoke_model.return_value = {"body": respbody}
+    model = BedrockChat(model_id="anthropic.claude-v2", client=client)
+
+    # should not throw an error
+    model.invoke("hello there")