test(providers): cover reasoning_content extraction in OpenAI compat provider

Add regression tests for the non-streaming (_parse dict branch) and
streaming (_parse_chunks dict and SDK-object branches) paths that extract
reasoning_content, ensuring the field is populated when present and None
when absent.

Signed-off-by: Lingao Meng <menglingao@xiaomi.com>

tests/providers/test_reasoning_content.py

@@ -0,0 +1,128 @@
+"""Tests for reasoning_content extraction in OpenAICompatProvider.
+
+Covers non-streaming (_parse) and streaming (_parse_chunks) paths for
+providers that return a reasoning_content field (e.g. MiMo, DeepSeek-R1).
+"""
+
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+# ── _parse: non-streaming ─────────────────────────────────────────────────
+
+
+def test_parse_dict_extracts_reasoning_content() -> None:
+    """reasoning_content at message level is surfaced in LLMResponse."""
+    with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
+        provider = OpenAICompatProvider()
+
+    response = {
+        "choices": [{
+            "message": {
+                "content": "42",
+                "reasoning_content": "Let me think step by step…",
+            },
+            "finish_reason": "stop",
+        }],
+        "usage": {"prompt_tokens": 5, "completion_tokens": 10, "total_tokens": 15},
+    }
+
+    result = provider._parse(response)
+
+    assert result.content == "42"
+    assert result.reasoning_content == "Let me think step by step…"
+
+
+def test_parse_dict_reasoning_content_none_when_absent() -> None:
+    """reasoning_content is None when the response doesn't include it."""
+    with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
+        provider = OpenAICompatProvider()
+
+    response = {
+        "choices": [{
+            "message": {"content": "hello"},
+            "finish_reason": "stop",
+        }],
+    }
+
+    result = provider._parse(response)
+
+    assert result.reasoning_content is None
+
+
+# ── _parse_chunks: streaming dict branch ─────────────────────────────────
+
+
+def test_parse_chunks_dict_accumulates_reasoning_content() -> None:
+    """reasoning_content deltas in dict chunks are joined into one string."""
+    chunks = [
+        {
+            "choices": [{
+                "finish_reason": None,
+                "delta": {"content": None, "reasoning_content": "Step 1. "},
+            }],
+        },
+        {
+            "choices": [{
+                "finish_reason": None,
+                "delta": {"content": None, "reasoning_content": "Step 2."},
+            }],
+        },
+        {
+            "choices": [{
+                "finish_reason": "stop",
+                "delta": {"content": "answer"},
+            }],
+        },
+    ]
+
+    result = OpenAICompatProvider._parse_chunks(chunks)
+
+    assert result.content == "answer"
+    assert result.reasoning_content == "Step 1. Step 2."
+
+
+def test_parse_chunks_dict_reasoning_content_none_when_absent() -> None:
+    """reasoning_content is None when no chunk contains it."""
+    chunks = [
+        {"choices": [{"finish_reason": "stop", "delta": {"content": "hi"}}]},
+    ]
+
+    result = OpenAICompatProvider._parse_chunks(chunks)
+
+    assert result.content == "hi"
+    assert result.reasoning_content is None
+
+
+# ── _parse_chunks: streaming SDK-object branch ────────────────────────────
+
+
+def _make_reasoning_chunk(reasoning: str | None, content: str | None, finish: str | None):
+    delta = SimpleNamespace(content=content, reasoning_content=reasoning, tool_calls=None)
+    choice = SimpleNamespace(finish_reason=finish, delta=delta)
+    return SimpleNamespace(choices=[choice], usage=None)
+
+
+def test_parse_chunks_sdk_accumulates_reasoning_content() -> None:
+    """reasoning_content on SDK delta objects is joined across chunks."""
+    chunks = [
+        _make_reasoning_chunk("Think… ", None, None),
+        _make_reasoning_chunk("Done.", None, None),
+        _make_reasoning_chunk(None, "result", "stop"),
+    ]
+
+    result = OpenAICompatProvider._parse_chunks(chunks)
+
+    assert result.content == "result"
+    assert result.reasoning_content == "Think… Done."
+
+
+def test_parse_chunks_sdk_reasoning_content_none_when_absent() -> None:
+    """reasoning_content is None when SDK deltas carry no reasoning_content."""
+    chunks = [_make_reasoning_chunk(None, "hello", "stop")]
+
+    result = OpenAICompatProvider._parse_chunks(chunks)
+
+    assert result.reasoning_content is None