add reasoning_tokens usage test for tool call (#18022)

python/sglang/test/tool_call_test_runner.py

@@ -23,6 +23,7 @@ class ToolCallTestParams:
     test_strict: bool = True
     test_multiturn: bool = True
     test_thinking: bool = False  # model-specific, e.g. DeepSeek
+    test_reasoning_usage: bool = False  # verify usage.reasoning_tokens > 0
     test_parallel: bool = True
 
 
@@ -225,6 +226,29 @@ def _test_thinking(client, model):
     assert "8" in content, f"expected '8' in content, got: {content}"
 
 
+def _test_reasoning_usage(client, model):
+    """With thinking enabled, usage.reasoning_tokens should be reported as > 0."""
+    thinking_body = {"thinking": {"type": "enabled", "budget_tokens": 1024}}
+    response = client.chat.completions.create(
+        model=model,
+        messages=[{"role": "user", "content": "What is 3 + 5?"}],
+        tools=[ADD_TOOL_STRICT],
+        tool_choice="required",
+        temperature=0.1,
+        extra_body=thinking_body,
+    )
+    usage = response.usage
+    assert usage is not None, "usage should not be None"
+    assert (
+        usage.reasoning_tokens and usage.reasoning_tokens > 0
+    ), f"expected reasoning_tokens > 0, got {usage.reasoning_tokens}"
+    if usage.completion_tokens_details:
+        detail_reasoning = usage.completion_tokens_details.get("reasoning_tokens", 0)
+        assert (
+            detail_reasoning > 0
+        ), f"expected completion_tokens_details.reasoning_tokens > 0, got {detail_reasoning}"
+
+
 def _test_parallel(client, model):
     """Single request should return multiple tool calls."""
     response = _call(
@@ -246,6 +270,7 @@ _TESTS = [
     ("strict", _test_strict, "test_strict"),
     ("multiturn", _test_multiturn, "test_multiturn"),
     ("thinking", _test_thinking, "test_thinking"),
+    ("reasoning_usage", _test_reasoning_usage, "test_reasoning_usage"),
     ("parallel", _test_parallel, "test_parallel"),
 ]