[Frontend] Respect Chat Completion parallel_tool_calls param (#26233)

Signed-off-by: Ben Browning <bbrownin@redhat.com>
Co-authored-by: Chauncey <chaunceyjiang@gmail.com>

tests/tool_use/test_parallel_tool_calls.py

@@ -212,3 +212,60 @@ async def test_parallel_tool_calls_with_results(
     assert finish_reason_count == 1
     assert len(chunks)
     assert "".join(chunks) == choice.message.content
+
+
+@pytest.mark.asyncio
+async def test_parallel_tool_calls_false(client: openai.AsyncOpenAI):
+    """
+    Ensure only one tool call is returned when parallel_tool_calls is False.
+    """
+
+    models = await client.models.list()
+    model_name: str = models.data[0].id
+    chat_completion = await client.chat.completions.create(
+        messages=MESSAGES_ASKING_FOR_PARALLEL_TOOLS,
+        temperature=0,
+        max_completion_tokens=200,
+        model=model_name,
+        tools=[WEATHER_TOOL, SEARCH_TOOL],
+        logprobs=False,
+        parallel_tool_calls=False,
+    )
+
+    stop_reason = chat_completion.choices[0].finish_reason
+    non_streamed_tool_calls = chat_completion.choices[0].message.tool_calls
+
+    # make sure only 1 tool call is present
+    assert len(non_streamed_tool_calls) == 1
+    assert stop_reason == "tool_calls"
+
+    # make the same request, streaming
+    stream = await client.chat.completions.create(
+        model=model_name,
+        messages=MESSAGES_ASKING_FOR_PARALLEL_TOOLS,
+        temperature=0,
+        max_completion_tokens=200,
+        tools=[WEATHER_TOOL, SEARCH_TOOL],
+        logprobs=False,
+        parallel_tool_calls=False,
+        stream=True,
+    )
+
+    finish_reason_count: int = 0
+    tool_call_id_count: int = 0
+
+    async for chunk in stream:
+        # if there's a finish reason make sure it's tools
+        if chunk.choices[0].finish_reason:
+            finish_reason_count += 1
+            assert chunk.choices[0].finish_reason == "tool_calls"
+
+        streamed_tool_calls = chunk.choices[0].delta.tool_calls
+        if streamed_tool_calls and len(streamed_tool_calls) > 0:
+            tool_call = streamed_tool_calls[0]
+            if tool_call.id:
+                tool_call_id_count += 1
+
+    # make sure only 1 streaming tool call is present
+    assert tool_call_id_count == 1
+    assert finish_reason_count == 1