[Frontend][responsesAPI][1/n] convert responses API tool input to chat completions tool format (#28231)

Signed-off-by: Andrew Xia <axia@fb.com>
Co-authored-by: Andrew Xia <axia@fb.com>
Co-authored-by: Chauncey <chaunceyjiang@gmail.com>

tests/entrypoints/test_responses_utils.py

@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from vllm.entrypoints.responses_utils import (
+    convert_tool_responses_to_completions_format,
+)
+
+
+class TestResponsesUtils:
+    """Tests for convert_tool_responses_to_completions_format function."""
+
+    def test_convert_tool_responses_to_completions_format(self):
+        """Test basic conversion of a flat tool schema to nested format."""
+        input_tool = {
+            "type": "function",
+            "name": "get_weather",
+            "description": "Get the current weather in a given location",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "location": {"type": "string"},
+                    "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]},
+                },
+                "required": ["location", "unit"],
+            },
+        }
+
+        result = convert_tool_responses_to_completions_format(input_tool)
+
+        assert result == {"type": "function", "function": input_tool}