test: assert the responses bridge forwards aws_region_name

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

tests/unit/completion_extras/test_responses_bridge_provider_propagation.py

@@ -0,0 +1,59 @@
+from datetime import datetime
+from unittest.mock import patch
+
+import pytest
+
+from litellm.completion_extras.litellm_responses_transformation.handler import (
+    ResponsesToCompletionBridgeHandler,
+)
+from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLogging
+from litellm.types.utils import ModelResponse
+
+MODEL = "openai.gpt-5.5"
+REGION = "us-east-2"
+
+
+def _bedrock_mantle_kwargs() -> dict:
+    messages = [{"role": "user", "content": "hi"}]
+    logging_obj = LiteLLMLogging(
+        litellm_call_id="test-call",
+        call_type="acompletion",
+        model=MODEL,
+        messages=messages,
+        function_id="fn-id",
+        stream=False,
+        start_time=datetime.now(),
+    )
+    return {
+        "model": MODEL,
+        "custom_llm_provider": "bedrock_mantle",
+        "messages": messages,
+        "optional_params": {},
+        "litellm_params": {
+            "aws_region_name": REGION,
+            "api_base": "https://bedrock-mantle.us-east-1.api.aws/v1",
+            "custom_llm_provider": "bedrock_mantle",
+        },
+        "headers": {},
+        "model_response": ModelResponse(),
+        "logging_obj": logging_obj,
+    }
+
+
+@pytest.mark.asyncio
+async def test_acompletion_forwards_aws_region_name_to_aresponses():
+    bridge = ResponsesToCompletionBridgeHandler()
+    cached = ModelResponse(id="chatcmpl-cached", model=MODEL)
+
+    async def _fake_aresponses(**kwargs):
+        _fake_aresponses.kwargs = kwargs
+        return cached
+
+    _fake_aresponses.kwargs = {}
+
+    with patch("litellm.aresponses", _fake_aresponses):
+        result = await bridge.acompletion(**_bedrock_mantle_kwargs())
+
+    assert result is cached
+    assert _fake_aresponses.kwargs["aws_region_name"] == REGION
+    assert _fake_aresponses.kwargs["custom_llm_provider"] == "bedrock_mantle"