test(13-01): add failing tests for video type detection

- 创建 conftest.py 共享 fixtures（MockAIClient, sample_segments）
- 创建 test_semantic_engine.py 包含 8 个测试用例
  - test_video_type_detection_from_title: 测试从标题推断类型
  - test_video_type_detection_from_category: 测试从分类推断类型
  - test_video_type_fallback_to_default: 测试默认类型回退
  - test_video_type_in_prompt: 测试类型出现在 Prompt 中
  - test_prompt_format: 测试 Prompt 格式
  - test_video_segment_model: 测试 VideoSegment 模型
  - test_segmentation_result_model: 测试 SegmentationResult 模型
  - test_model_validation: 测试字段验证

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_semantic_engine.py

@@ -0,0 +1,129 @@
+"""测试语义分段引擎"""
+
+import pytest
+
+from kb_workflow.srt.semantic_engine import (
+    VideoSegment,
+    SegmentationResult,
+    SemanticSegmentationEngine
+)
+
+
+class TestVideoTypeDetection:
+    """测试视频类型识别功能"""
+
+    def test_video_type_detection_from_title(self):
+        """测试从标题推断视频类型"""
+        # 知识类 - 从标题推断
+        metadata_edu = {"title": "Python编程教程", "category": "教育"}
+        engine = SemanticSegmentationEngine()
+        video_type = engine._infer_video_type(metadata_edu)
+        assert video_type == "知识类"
+
+        # 知识类 - 包含"课程"
+        metadata_course = {"title": "机器学习课程", "category": ""}
+        video_type = engine._infer_video_type(metadata_course)
+        assert video_type == "知识类"
+
+    def test_video_type_detection_from_category(self):
+        """测试从分类推断视频类型"""
+        # 故事类 - 从分类推断
+        metadata_movie = {"title": "星际穿越", "category": "影视"}
+        engine = SemanticSegmentationEngine()
+        video_type = engine._infer_video_type(metadata_movie)
+        assert video_type == "故事类"
+
+        # 访谈类 - 从标签推断
+        metadata_interview = {"title": "名人访谈", "tags": ["访谈", "对话"]}
+        video_type = engine._infer_video_type(metadata_interview)
+        assert video_type == "访谈类"
+
+    def test_video_type_fallback_to_default(self):
+        """测试元数据缺失时使用默认类型"""
+        # 空元数据
+        engine = SemanticSegmentationEngine()
+        video_type = engine._infer_video_type({})
+        assert video_type == "知识类"  # 默认类型
+
+        # 无效元数据
+        video_type = engine._infer_video_type({"title": "", "category": ""})
+        assert video_type == "知识类"
+
+
+class TestVideoTypeInPrompt:
+    """测试视频类型在 Prompt 中的使用"""
+
+    def test_video_type_in_prompt(self):
+        """测试 Prompt 包含视频类型信息"""
+        engine = SemanticSegmentationEngine()
+        metadata = {"title": "机器学习教程", "category": "教育"}
+
+        prompt = engine._build_prompt("测试内容", metadata)
+
+        assert "视频类型" in prompt or "知识类" in prompt
+        assert "机器学习教程" in prompt
+
+    def test_prompt_format(self):
+        """测试 Prompt 格式正确"""
+        engine = SemanticSegmentationEngine()
+        content = "这是测试内容"
+        metadata = {"title": "测试视频"}
+
+        prompt = engine._build_prompt(content, metadata)
+
+        assert "请分析以下视频字幕" in prompt or "字幕内容" in prompt
+        assert content in prompt
+
+
+class TestPydanticModels:
+    """测试 Pydantic 模型验证"""
+
+    def test_video_segment_model(self):
+        """测试 VideoSegment 模型"""
+        # 创建完整分段
+        segment = VideoSegment(
+            title="机器学习概述",
+            content="机器学习是人工智能的一个分支",
+            start_index=1,
+            end_index=5
+        )
+        assert segment.title == "机器学习概述"
+        assert segment.content == "机器学习是人工智能的一个分支"
+        assert segment.start_index == 1
+        assert segment.end_index == 5
+
+        # 创建无标题分段（title 可选）
+        segment_no_title = VideoSegment(
+            content="测试内容",
+            start_index=1,
+            end_index=3
+        )
+        assert segment_no_title.title is None
+
+    def test_segmentation_result_model(self):
+        """测试 SegmentationResult 模型"""
+        segments = [
+            VideoSegment(title="第一章", content="内容1", start_index=1, end_index=5),
+            VideoSegment(title="第二章", content="内容2", start_index=6, end_index=10)
+        ]
+
+        result = SegmentationResult(
+            video_type="知识类",
+            segments=segments,
+            actual_segment_count=2
+        )
+
+        assert result.video_type == "知识类"
+        assert len(result.segments) == 2
+        assert result.actual_segment_count == 2
+
+    def test_model_validation(self):
+        """测试模型字段验证"""
+        # 缺少必填字段应该抛出异常
+        with pytest.raises(Exception):  # Pydantic ValidationError
+            VideoSegment(
+                title="测试",
+                # 缺少 content
+                start_index=1,
+                end_index=3
+            )