fix function calling type to follow open ai, add tests

tests/local_testing/test_function_calling.py

@@ -769,3 +769,61 @@ async def test_function_calling_with_dbrx():
         json_data = json.loads(mock_completion.call_args.kwargs["data"])
         assert "tools" in json_data
         assert "tool_choice" in json_data
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model",
+    [
+        "gpt-4-1106-preview",
+        "mistral/mistral-small-latest",
+    ],
+)
+async def test_function_calling_tool_type(model):
+    """
+    Test the API's response when streaming tool calls. 
+    - The first streamed chunk contains a tool call with an ID and type "function".
+    - Subsequent chunks may only contain arguments, with ID and type being None.
+    """
+    response = completion(
+        model=model, 
+        messages=[{
+            "role": "user", 
+            "content": "Search for recent AI breakthroughs"
+        }],
+            tools=[{
+                "type": "function",
+                "function": {
+                    "name": "web_search",
+                    "description": "Searches the web",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {
+                            "query": {"type": "string"}
+                        },
+                        "required": ["query"]
+                    }
+                }
+            }],
+        stream=True,
+        temperature=0.00000001
+    )
+
+
+    async for chunk in response:
+        print(json.dumps(chunk, indent=2, default=str))
+        if "choices" not in chunk or not chunk.choices:
+            raise ValueError("Unexpected chunk structure: 'choices' missing or empty")
+
+        delta = chunk.choices[0].delta
+        tool_calls = getattr(delta, "tool_calls", None)
+
+        if not tool_calls or not isinstance(tool_calls, list):
+            continue
+
+        tool_call = tool_calls[0]
+        id = getattr(tool_call, "id", None)
+        type = getattr(tool_call, "type", None)
+
+        if id:
+            assert type == "function", f"Expected type 'function' for id {id}, got '{type}'"