test: 补充缺失的核心模块测试，统一CLI测试行为

新增测试文件：
- tests/test_core/test_parser.py - 测试 parse_input/process_content/output_result
- tests/test_core/test_markdown_extra.py - 测试 extract_title_content/search_markdown
- tests/test_utils/test_encoding_detection.py - 测试编码检测模块
- tests/test_readers/test_html_downloader.py - 测试HTML下载器

修改：
- tests/conftest.py - 移除pytest.skip()，所有CLI测试在缺少依赖时直接失败（与HTML测试行为一致）

tests/test_core/test_markdown_extra.py

@@ -0,0 +1,233 @@
+"""测试 markdown 模块的高级功能（extract_title_content, search_markdown）。"""
+
+import pytest
+
+from core.markdown import extract_title_content, search_markdown
+
+
+class TestExtractTitleContent:
+    """测试 extract_title_content 函数。"""
+
+    def test_extract_simple_title(self):
+        """测试提取简单标题。"""
+        markdown = """# 目标标题
+
+这是标题下的内容。
+第二段内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "# 目标标题" in result
+        assert "这是标题下的内容" in result
+
+    def test_extract_with_subtitles(self):
+        """测试提取包含子标题的内容。"""
+        markdown = """# 目标标题
+
+这是标题下的内容。
+
+## 子标题
+
+子标题下的内容。
+
+### 孙子标题
+
+更深层的内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "# 目标标题" in result
+        assert "## 子标题" in result
+        assert "### 孙子标题" in result
+
+    def test_extract_stop_at_sibling_title(self):
+        """测试在同级标题处停止。"""
+        markdown = """# 目标标题
+
+目标内容。
+
+# 另一个标题
+
+另一个内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "# 目标标题" in result
+        assert "目标内容" in result
+        assert "# 另一个标题" not in result
+
+    def test_extract_with_parent_titles(self):
+        """测试包含父级标题。"""
+        markdown = """# 父级标题
+
+父级内容。
+
+## 目标标题
+
+目标内容。
+
+### 子标题
+
+子内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "# 父级标题" in result
+        assert "## 目标标题" in result
+        assert "### 子标题" in result
+
+    def test_extract_multiple_matches(self):
+        """测试多个匹配标题的情况。"""
+        markdown = """# 第一章
+
+## 目标标题
+
+第一章的目标内容。
+
+# 第二章
+
+## 目标标题
+
+第二章的目标内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "第一章的目标内容" in result
+        assert "第二章的目标内容" in result
+        assert "---" in result
+
+    def test_title_not_found(self):
+        """测试标题不存在的情况。"""
+        markdown = "# 其他标题\n内容"
+
+        result = extract_title_content(markdown, "不存在的标题")
+
+        assert result is None
+
+    def test_deep_nested_title(self):
+        """测试深层嵌套标题。"""
+        markdown = """# H1
+
+## H2
+
+### H3
+
+#### 目标标题
+
+目标内容。"""
+
+        result = extract_title_content(markdown, "目标标题")
+
+        assert result is not None
+        assert "# H1" in result
+        assert "## H2" in result
+        assert "### H3" in result
+        assert "#### 目标标题" in result
+
+
+class TestSearchMarkdown:
+    """测试 search_markdown 函数。"""
+
+    def test_search_simple_pattern(self):
+        """测试简单搜索模式。"""
+        content = """第一行
+第二行
+包含关键词的行
+第四行"""
+
+        result = search_markdown(content, "关键词", context_lines=0)
+
+        assert result is not None
+        assert "关键词" in result
+
+    def test_search_with_context(self):
+        """测试带上下文的搜索。"""
+        content = """行1
+行2
+关键词行
+行4
+行5"""
+
+        result = search_markdown(content, "关键词", context_lines=1)
+
+        assert result is not None
+        assert "关键词" in result
+        assert "行2" in result or "行4" in result
+
+    def test_search_no_match(self):
+        """测试无匹配的情况。"""
+        content = "普通内容"
+
+        result = search_markdown(content, "不存在的内容", context_lines=0)
+
+        assert result is None
+
+    def test_search_empty_content(self):
+        """测试空内容。"""
+        result = search_markdown("", "关键词", context_lines=0)
+
+        assert result is None
+
+    def test_search_invalid_regex(self):
+        """测试无效正则表达式。"""
+        content = "内容"
+
+        result = search_markdown(content, "[invalid", context_lines=0)
+
+        assert result is None
+
+    def test_search_negative_context(self):
+        """测试负的上下文行数。"""
+        content = "内容"
+
+        with pytest.raises(ValueError):
+            search_markdown(content, "内容", context_lines=-1)
+
+    def test_search_multiple_matches_merged(self):
+        """测试多个匹配合并。"""
+        content = """行1
+行2
+匹配1
+行4
+行5
+匹配2
+行7
+行8"""
+
+        result = search_markdown(content, "匹配", context_lines=1)
+
+        assert result is not None
+        assert "匹配1" in result
+        assert "匹配2" in result
+
+    def test_search_ignore_blank_lines_in_context(self):
+        """测试上下文计算忽略空行。"""
+        content = """行1
+
+行2
+关键词
+
+行4
+行5"""
+
+        result = search_markdown(content, "关键词", context_lines=1)
+
+        assert result is not None
+        assert "关键词" in result
+
+    def test_search_with_regex(self):
+        """测试使用正则表达式搜索。"""
+        content = """apple
+banana
+cherry
+date"""
+
+        result = search_markdown(content, "^b", context_lines=0)
+
+        assert result is not None
+        assert "banana" in result