[Frontend] Add streaming tool-call support to Responses API (non-Harmony)

tests/entrypoints/openai/test_responses_streaming_tool_calls.py

@@ -0,0 +1,101 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+import pytest_asyncio
+from openai.types.responses import (
+    ResponseFunctionCallArgumentsDeltaEvent,
+    ResponseFunctionCallArgumentsDoneEvent,
+    ResponseOutputItemAddedEvent,
+)
+
+from tests.utils import RemoteOpenAIServer
+
+MODEL_NAME = "Qwen/Qwen3-0.6B"
+
+INTEGRATION_TOOLS = [
+    {
+        "type": "function",
+        "name": "get_current_weather",
+        "description": "Get the current weather in a given location",
+        "parameters": {
+            "type": "object",
+            "properties": {
+                "city": {"type": "string"},
+                "country": {"type": "string"},
+                "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]},
+            },
+            "required": ["city", "country", "unit"],
+        },
+    }
+]
+
+
+@pytest.fixture(scope="module")
+def responses_server():
+    args = [
+        "--dtype",
+        "half",
+        "--enable-auto-tool-choice",
+        "--structured-outputs-config.backend",
+        "xgrammar",
+        "--tool-call-parser",
+        "hermes",
+        "--reasoning-parser",
+        "qwen3",
+        "--gpu-memory-utilization",
+        "0.3",
+        "--max-model-len",
+        "2048",
+    ]
+    with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:
+        yield remote_server
+
+
+@pytest_asyncio.fixture
+async def responses_client(responses_server):
+    async with responses_server.get_async_client() as async_client:
+        yield async_client
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "tool_choice",
+    [
+        "auto",
+    ],
+)
+async def test_responses_streaming_tool_calls_e2e(responses_client, tool_choice):
+    stream = await responses_client.responses.create(
+        model=MODEL_NAME,
+        input=(
+            "Use the weather tool to get the temperature for Berlin, Germany in "
+            "fahrenheit"
+        ),
+        tools=INTEGRATION_TOOLS,
+        tool_choice=tool_choice,
+        stream=True,
+        temperature=0,
+    )
+
+    added_event = None
+    arg_chunks: list[str] = []
+    final_arguments: str | None = None
+    async for event in stream:
+        if (
+            isinstance(event, ResponseOutputItemAddedEvent)
+            and getattr(event.item, "type", None) == "function_call"
+        ):
+            added_event = event
+        if isinstance(event, ResponseFunctionCallArgumentsDeltaEvent):
+            arg_chunks.append(event.delta)
+        if isinstance(event, ResponseFunctionCallArgumentsDoneEvent):
+            final_arguments = event.arguments
+
+    assert added_event is not None
+    assert final_arguments is not None
+    assert final_arguments == "".join(arg_chunks)
+    args_text = final_arguments.lower()
+    assert "berlin" in args_text
+    assert "germany" in args_text
+    assert "fahrenheit" in args_text