diff --git a/backend/tests/test_html_generator.py b/backend/tests/test_html_generator.py
deleted file mode 100644
index fbbc1e0..0000000
--- a/backend/tests/test_html_generator.py
+++ /dev/null
@@ -1,54 +0,0 @@
-# test_html_generator.py
-import pytest
-
-# 使用实际实现的 HTMLGenerator
-from app.services.content.html_generator import HTMLGenerator
-
-def test_filter_banned_tags_zhihu():
-    """知乎HTML标签过滤"""
-    generator = HTMLGenerator()
-    html = generator.generate(
-        content="<script>alert(1)</script><p>这是内容</p>",
-        platform="zhihu"
-    )
-    assert "<script>" not in html
-    assert "<p>这是内容</p>" in html
-
-def test_filter_banned_tags_wechat():
-    """微信公众号HTML过滤"""
-    generator = HTMLGenerator()
-    html = generator.generate(
-        content="<a href='http://baidu.com'>外部链接</a><p>内容</p>",
-        platform="wechat"
-    )
-    # 微信公众号禁止外部链接
-    assert "http://baidu.com" not in html
-
-def test_convert_to_markdown():
-    """Markdown转换"""
-    generator = HTMLGenerator()
-    md = generator.to_markdown("<h1>标题</h1><p>段落</p>")
-    assert "# 标题" in md
-    assert "段落" in md
-
-def test_convert_to_plain():
-    """纯文本转换"""
-    generator = HTMLGenerator()
-    plain = generator.to_plain("<h1>标题</h1><p>段落<b>加粗</b></p>")
-    assert "标题" in plain
-    assert "段落" in plain
-    assert "<" not in plain  # 不应包含HTML标签
-
-def test_multi_format_output():
-    """多格式同时输出"""
-    generator = HTMLGenerator()
-    html = generator.generate("<p>内容</p>", "zhihu", "html")
-    md = generator.to_markdown("<p>内容</p>")
-    plain = generator.to_plain("<p>内容</p>")
-    
-    assert html is not None
-    assert md is not None
-    assert plain is not None
-    assert len(html) > 0
-    assert len(md) > 0
-    assert len(plain) > 0
diff --git a/backend/tests/test_config.py b/backend/tests/test_infrastructure/test_config.py
similarity index 100%
rename from backend/tests/test_config.py
rename to backend/tests/test_infrastructure/test_config.py
diff --git a/backend/tests/test_database_exception_handling.py b/backend/tests/test_infrastructure/test_database_exception_handling.py
similarity index 100%
rename from backend/tests/test_database_exception_handling.py
rename to backend/tests/test_infrastructure/test_database_exception_handling.py
diff --git a/backend/tests/test_database_migration.py b/backend/tests/test_infrastructure/test_database_migration.py
similarity index 100%
rename from backend/tests/test_database_migration.py
rename to backend/tests/test_infrastructure/test_database_migration.py
diff --git a/backend/tests/test_performance.py b/backend/tests/test_infrastructure/test_performance.py
similarity index 100%
rename from backend/tests/test_performance.py
rename to backend/tests/test_infrastructure/test_performance.py
diff --git a/backend/tests/test_infrastructure/test_rate_limit.py b/backend/tests/test_infrastructure/test_rate_limit.py
new file mode 100644
index 0000000..ecb8704
--- /dev/null
+++ b/backend/tests/test_infrastructure/test_rate_limit.py
@@ -0,0 +1,181 @@
+"""限流中间件测试 — 覆盖内存后端和 Redis 后端降级场景。"""
+import asyncio
+import time
+
+import pytest
+
+from app.middleware.rate_limit import (
+    MemoryRateLimitBackend,
+    RateLimitBackend,
+    RedisRateLimitBackend,
+    _create_backend,
+)
+
+
+# ---------------------------------------------------------------------------
+# MemoryRateLimitBackend 测试
+# ---------------------------------------------------------------------------
+
+class TestMemoryRateLimitBackend:
+    """内存后端核心逻辑测试。"""
+
+    def setup_method(self):
+        self.backend = MemoryRateLimitBackend()
+
+    @pytest.mark.asyncio
+    async def test_under_limit_not_blocked(self):
+        """未达限流阈值时不被限流。"""
+        now = time.time()
+        for i in range(5):
+            result = await self.backend.is_rate_limited("test:key", now + i * 0.001, 5, 60)
+            assert result is False
+
+    @pytest.mark.asyncio
+    async def test_at_limit_blocked(self):
+        """达到限流阈值后被限流。"""
+        now = time.time()
+        # 先发送 max_requests 个请求
+        for i in range(5):
+            await self.backend.is_rate_limited("test:key", now + i * 0.001, 5, 60)
+        # 第 6 个请求应被限流
+        result = await self.backend.is_rate_limited("test:key", now + 0.006, 5, 60)
+        assert result is True
+
+    @pytest.mark.asyncio
+    async def test_window_expiry_allows_new_requests(self):
+        """窗口过期后允许新请求。"""
+        now = time.time()
+        # 在窗口开始时发送 5 个请求
+        for i in range(5):
+            await self.backend.is_rate_limited("test:key", now + i * 0.001, 5, 60)
+        # 窗口过期后发送新请求
+        new_now = now + 61  # 超过 60 秒窗口
+        result = await self.backend.is_rate_limited("test:key", new_now, 5, 60)
+        assert result is False
+
+    @pytest.mark.asyncio
+    async def test_different_keys_independent(self):
+        """不同 key 的限流状态独立。"""
+        now = time.time()
+        # key1 达到限流
+        for i in range(5):
+            await self.backend.is_rate_limited("key1", now + i * 0.001, 5, 60)
+        result1 = await self.backend.is_rate_limited("key1", now + 0.006, 5, 60)
+        assert result1 is True
+        # key2 不受限流影响
+        result2 = await self.backend.is_rate_limited("key2", now, 5, 60)
+        assert result2 is False
+
+    @pytest.mark.asyncio
+    async def test_reset_clears_key(self):
+        """reset 清除指定 key 的限流状态。"""
+        now = time.time()
+        for i in range(5):
+            await self.backend.is_rate_limited("test:key", now + i * 0.001, 5, 60)
+        # 限流中
+        result = await self.backend.is_rate_limited("test:key", now + 0.006, 5, 60)
+        assert result is True
+        # 重置后不再限流
+        await self.backend.reset("test:key")
+        result = await self.backend.is_rate_limited("test:key", now + 0.007, 5, 60)
+        assert result is False
+
+    @pytest.mark.asyncio
+    async def test_cleanup_removes_expired_entries(self):
+        """后台清理任务移除过期记录。"""
+        now = time.time()
+        # 添加一些记录
+        await self.backend.is_rate_limited("old_key", now - 3700, 5, 60)
+        await self.backend.is_rate_limited("recent_key", now, 5, 60)
+        # 模拟清理
+        self.backend._requests["old_key"] = [now - 3700]
+        self.backend._requests["recent_key"] = [now]
+        # 手动触发清理逻辑
+        expired_keys = []
+        for key in list(self.backend._requests.keys()):
+            self.backend._requests[key] = [t for t in self.backend._requests[key] if now - t < 3600]
+            if not self.backend._requests[key]:
+                expired_keys.append(key)
+        for key in expired_keys:
+            del self.backend._requests[key]
+        assert "old_key" not in self.backend._requests
+        assert "recent_key" in self.backend._requests
+
+
+# ---------------------------------------------------------------------------
+# RedisRateLimitBackend 测试（无 Redis 连接时的降级行为）
+# ---------------------------------------------------------------------------
+
+class TestRedisRateLimitBackendFallback:
+    """Redis 后端在连接失败时的降级行为。"""
+
+    @pytest.mark.asyncio
+    async def test_redis_unavailable_allows_request(self):
+        """Redis 不可用时放行请求（不阻塞服务）。"""
+        backend = RedisRateLimitBackend("redis://nonexistent:6379/0")
+        now = time.time()
+        # Redis 连接失败时应返回 False（不被限流）
+        result = await backend.is_rate_limited("test:key", now, 5, 60)
+        assert result is False
+
+    @pytest.mark.asyncio
+    async def test_redis_reset_silently_fails(self):
+        """Redis reset 失败时静默处理。"""
+        backend = RedisRateLimitBackend("redis://nonexistent:6379/0")
+        # 不应抛出异常
+        await backend.reset("test:key")
+
+
+# ---------------------------------------------------------------------------
+# Backend 工厂函数测试
+# ---------------------------------------------------------------------------
+
+class TestCreateBackend:
+    """_create_backend 工厂函数测试。"""
+
+    def test_default_creates_memory_backend(self, monkeypatch):
+        """默认配置创建内存后端。"""
+        monkeypatch.setattr("app.middleware.rate_limit.settings.RATE_LIMIT_BACKEND", "memory")
+        backend = _create_backend()
+        assert isinstance(backend, MemoryRateLimitBackend)
+
+    def test_redis_with_empty_url_falls_back_to_memory(self, monkeypatch):
+        """RATE_LIMIT_BACKEND=redis 但 REDIS_URL 为空时降级到内存。"""
+        monkeypatch.setattr("app.middleware.rate_limit.settings.RATE_LIMIT_BACKEND", "redis")
+        monkeypatch.setattr("app.middleware.rate_limit.settings.REDIS_URL", "")
+        backend = _create_backend()
+        assert isinstance(backend, MemoryRateLimitBackend)
+
+    def test_redis_with_url_creates_redis_backend(self, monkeypatch):
+        """RATE_LIMIT_BACKEND=redis 且 REDIS_URL 非空时创建 Redis 后端。"""
+        monkeypatch.setattr("app.middleware.rate_limit.settings.RATE_LIMIT_BACKEND", "redis")
+        monkeypatch.setattr("app.middleware.rate_limit.settings.REDIS_URL", "redis://localhost:6379/0")
+        backend = _create_backend()
+        assert isinstance(backend, RedisRateLimitBackend)
+
+    def test_unknown_backend_defaults_to_memory(self, monkeypatch):
+        """未知后端类型默认使用内存。"""
+        monkeypatch.setattr("app.middleware.rate_limit.settings.RATE_LIMIT_BACKEND", "unknown")
+        backend = _create_backend()
+        assert isinstance(backend, MemoryRateLimitBackend)
+
+
+# ---------------------------------------------------------------------------
+# RateLimitBackend 接口测试
+# ---------------------------------------------------------------------------
+
+class TestRateLimitBackendInterface:
+    """验证 RateLimitBackend 抽象接口。"""
+
+    def test_cannot_instantiate_abstract_class(self):
+        """不能直接实例化抽象类。"""
+        with pytest.raises(TypeError):
+            RateLimitBackend()
+
+    def test_memory_backend_is_subclass(self):
+        """MemoryRateLimitBackend 是 RateLimitBackend 的子类。"""
+        assert issubclass(MemoryRateLimitBackend, RateLimitBackend)
+
+    def test_redis_backend_is_subclass(self):
+        """RedisRateLimitBackend 是 RateLimitBackend 的子类。"""
+        assert issubclass(RedisRateLimitBackend, RateLimitBackend)
diff --git a/backend/tests/test_scheduler.py b/backend/tests/test_infrastructure/test_scheduler.py
similarity index 100%
rename from backend/tests/test_scheduler.py
rename to backend/tests/test_infrastructure/test_scheduler.py
diff --git a/backend/tests/test_security.py b/backend/tests/test_infrastructure/test_security.py
similarity index 100%
rename from backend/tests/test_security.py
rename to backend/tests/test_infrastructure/test_security.py
diff --git a/backend/tests/test_rule_validator.py b/backend/tests/test_rule_validator.py
deleted file mode 100644
index d04de43..0000000
--- a/backend/tests/test_rule_validator.py
+++ /dev/null
@@ -1,105 +0,0 @@
-# test_rule_validator.py
-import pytest
-from app.services.distribution.platform_rules import PLATFORM_RULES
-from app.services.content.rule_validator import RuleValidator, ValidationIssue, ValidationResult, AI_Pattern
-
-def test_validate_title_length_pass():
-    """标题长度符合规则时返回passed"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="这是一篇关于AI医疗的深度分析文章...",
-        title="AI医疗的发展趋势与未来展望",  # 符合知乎10-30要求
-        platform="zhihu"
-    )
-    assert result.is_valid == True
-    assert any("标题长度合规" in p or "合规" in p for p in result.passed)
-
-def test_validate_title_length_fail():
-    """标题长度超出限制时返回issue"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="内容",
-        title="这个标题太长了超过了三十个字符的限制了哈哈哈哈哈哈",  # 超过微信公众号22字限制
-        platform="wechat"  # 微信公众号限制22字
-    )
-    assert result.is_valid == False
-    assert any("超过" in i.message for i in result.issues if i.severity == "high")
-
-def test_validate_content_length_pass():
-    """内容长度符合规则时返回passed"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="A" * 1500,  # 1500字，符合知乎500-50000要求
-        title="测试标题",
-        platform="zhihu"
-    )
-    assert result.score >= 80
-
-def test_validate_content_length_fail():
-    """内容超长返回issue"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="A" * 30000,  # 30000字，微信公众号限制20000
-        title="测试标题",
-        platform="wechat"
-    )
-    assert any("超过" in i.message for i in result.issues if i.severity == "high")
-
-def test_detect_ai_patterns_banned_words():
-    """检测禁用词"""
-    validator = RuleValidator()
-    result = validator.detect_ai_patterns(
-        content="首先，其次，最后，总而言之，总之，总之",
-        platform="zhihu"
-    )
-    assert len(result) > 0
-    assert any("首先" in r.pattern or "总之" in r.pattern for r in result)
-
-def test_detect_ai_patterns_banned_structures():
-    """检测禁用结构"""
-    validator = RuleValidator()
-    result = validator.detect_ai_patterns(
-        content="第一，观点一。第二，观点二。第三，观点三。",
-        platform="zhihu"
-    )
-    assert len(result) > 0
-
-def test_validate_zhihu_specific_rules():
-    """知乎特定规则"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="这是一个专业回答",
-        title="专业回答",
-        platform="zhihu"
-    )
-    # 知乎应检查营销用语
-    assert result.score > 0
-
-def test_validate_wechat_specific_rules():
-    """微信公众号特定规则"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="点击购买，限时优惠",
-        title="限时优惠",
-        platform="wechat"
-    )
-    # 微信公众号应检测诱导分享
-    assert any("诱导" in i.message or "营销" in i.message for i in result.issues)
-
-def test_validate_xiaohongshu_rules():
-    """小红书特定规则"""
-    validator = RuleValidator()
-    result = validator.validate(
-        content="微信公众号搜索xxx获取更多内容",
-        title="种草笔记",
-        platform="xiaohongshu"
-    )
-    # 小红书应检测跨平台引流
-    assert any("引流" in i.message or "平台" in i.message for i in result.issues)
-
-def test_get_optimization_tips():
-    """获取优化建议"""
-    validator = RuleValidator()
-    tips = validator.get_optimization_tips("zhihu")
-    assert len(tips) > 0
-    assert any(isinstance(tip, str) for tip in tips)
diff --git a/backend/tests/test_sensitive_filter.py b/backend/tests/test_sensitive_filter.py
deleted file mode 100644
index 6aef862..0000000
--- a/backend/tests/test_sensitive_filter.py
+++ /dev/null
@@ -1,57 +0,0 @@
-import pytest
-
-# 导入实际的 SensitiveFilter 实现
-from app.services.content.sensitive_filter import SensitiveFilter
-
-
-def test_filter_politics_words():
-    """政治敏感词被替换为占位符"""
-    filter = SensitiveFilter()
-    result = filter.filter(
-        content="这是一个关于台湾问题的分析",
-        platform="zhihu"
-    )
-    assert "**" in result.filtered_content
-    assert len(result.found_words) > 0
-    assert result.found_words[0].category == "politics"
-
-def test_filter_medical_words():
-    """医疗敏感词处理"""
-    filter = SensitiveFilter()
-    result = filter.filter(
-        content="这个药品效果很好",
-        platform="wechat"
-    )
-    # 医疗类敏感词应被检测
-    assert result.found_words is not None
-
-def test_filter_finance_words():
-    """金融敏感词处理"""
-    filter = SensitiveFilter()
-    result = filter.filter(
-        content="年化收益率10%",
-        platform="zhihu"
-    )
-    # 金融敏感词检测
-    assert result.found_words is not None
-
-def test_filter_multiple_categories():
-    """多分类同时过滤"""
-    filter = SensitiveFilter()
-    result = filter.filter(
-        content="这是内容包含政治和医疗敏感词的内容",
-        platform="wechat"
-    )
-    categories = [w.category for w in result.found_words]
-    assert len(set(categories)) >= 1  # 至少检测到一个分类
-
-def test_add_custom_words():
-    """自定义敏感词添加"""
-    filter = SensitiveFilter()
-    filter.add_custom_words("custom", ["敏感词1", "敏感词2"])
-    
-    result = filter.filter(
-        content="这是一段包含敏感词1的内容",
-        platform="zhihu"
-    )
-    assert "敏感词1" not in result.filtered_content
\ No newline at end of file
diff --git a/backend/tests/test_seo_optimizer.py b/backend/tests/test_seo_optimizer.py
deleted file mode 100644
index dd174cd..0000000
--- a/backend/tests/test_seo_optimizer.py
+++ /dev/null
@@ -1,61 +0,0 @@
-# test_seo_optimizer.py
-import pytest
-
-# 导入实际实现的 SEOOptimizer
-from app.services.content.seo_optimizer import SEOOptimizer
-
-def test_get_keyword_density():
-    """关键词密度计算"""
-    optimizer = SEOOptimizer()
-    content = "AI医疗AI医疗AI医疗"  # 5个字，AI医疗出现3次
-    density = optimizer.get_keyword_density(content, "AI医疗")
-    # 密度计算：(3 * 4) / 15 ≈ 0.8 (约80%)
-    assert density > 0
-
-def test_adjust_keyword_density():
-    """密度调整到推荐范围"""
-    optimizer = SEOOptimizer()
-    result = optimizer.optimize(
-        content="AI医疗是未来发展趋势。随着人工智能技术的不断进步，医疗领域正在经历智能化变革。智能诊断系统能够分析海量医学数据，为医生提供辅助决策支持，提高诊疗效率和准确性，改善患者就医体验，推动医疗资源的优化配置和行业升级，促进整个医疗生态的可持续发展，提升医疗服务质量与管理水平。",
-        title="AI医疗",
-        platform="zhihu",  # 推荐密度 1-3%
-        keyword="AI医疗"
-    )
-    # 优化后密度应在推荐范围内
-    assert result.density >= 1.0
-    assert result.density <= 3.0
-
-def test_optimize_keyword_position():
-    """关键词位置优化"""
-    optimizer = SEOOptimizer()
-    result = optimizer.optimize(
-        content="这是一篇关于人工智能医疗的文章",
-        title="文章标题",
-        platform="zhihu",
-        keyword="AI医疗"
-    )
-    # 应建议在标题中添加关键词
-    assert result.suggestions is not None
-    assert len(result.suggestions) > 0
-
-def test_optimize_multiple_keywords():
-    """多关键词处理"""
-    optimizer = SEOOptimizer()
-    result = optimizer.optimize(
-        content="人工智能和机器学习是热门技术",
-        title="技术文章",
-        platform="zhihu",
-        keyword="人工智能"
-    )
-    assert result.optimized_content is not None
-
-def test_seo_tips_generation():
-    """SEO建议生成"""
-    optimizer = SEOOptimizer()
-    result = optimizer.optimize(
-        content="内容",
-        title="标题",
-        platform="zhihu"
-    )
-    assert result.tips is not None
-    assert len(result.tips) > 0
diff --git a/backend/tests/test_platform_adapters.py b/backend/tests/test_services/test_platform_adapters.py
similarity index 100%
rename from backend/tests/test_platform_adapters.py
rename to backend/tests/test_services/test_platform_adapters.py
diff --git a/backend/tests/test_services/test_platform_rules.py b/backend/tests/test_services/test_platform_rules.py
index 8b63e82..dd2fc48 100644
--- a/backend/tests/test_services/test_platform_rules.py
+++ b/backend/tests/test_services/test_platform_rules.py
@@ -91,6 +91,61 @@ class TestPlatformRuleEngine:
         tips = engine.get_optimization_tips("unknown_xyz")
         assert tips == []
 
+    # --- 标签验证测试 ---
+
+    def test_validate_tags_within_range(self, engine):
+        """标签数量在范围内验证通过"""
+        title = "合规标题测试"
+        content = "这是符合要求的内容。" * 50
+        result = engine.validate_content(content, title, "wechat", tags=["标签1", "标签2", "标签3"])
+
+        tag_issues = [i for i in result["issues"] if i.get("category") == "tag_count"]
+        assert len(tag_issues) == 0
+
+    def test_validate_tags_below_minimum(self, engine):
+        """标签数量低于最低要求返回 medium issue"""
+        title = "合规标题测试"
+        content = "这是符合要求的内容。" * 50
+        result = engine.validate_content(content, title, "wechat", tags=[])
+
+        tag_issues = [i for i in result["issues"] if i.get("category") == "tag_count"]
+        assert len(tag_issues) > 0
+        assert tag_issues[0]["severity"] == "medium"
+        assert "低于最低要求" in tag_issues[0]["message"]
+
+    def test_validate_tags_exceed_maximum(self, engine):
+        """标签数量超过限制返回 high issue"""
+        title = "合规标题测试"
+        content = "这是符合要求的内容。" * 50
+        # 微信 max_tags=10，传入 15 个
+        many_tags = [f"标签{i}" for i in range(15)]
+        result = engine.validate_content(content, title, "wechat", tags=many_tags)
+
+        tag_issues = [i for i in result["issues"] if i.get("category") == "tag_count"]
+        assert len(tag_issues) > 0
+        assert tag_issues[0]["severity"] == "high"
+        assert "超过限制" in tag_issues[0]["message"]
+
+    def test_validate_tags_as_comma_separated_string(self, engine):
+        """标签为逗号分隔字符串时正确解析"""
+        title = "合规标题测试"
+        content = "这是符合要求的内容。" * 50
+        result = engine.validate_content(content, title, "wechat", tags="标签1,标签2,标签3")
+
+        tag_issues = [i for i in result["issues"] if i.get("category") == "tag_count"]
+        assert len(tag_issues) == 0
+
+    def test_validate_no_tags_treated_as_zero(self, engine):
+        """无标签时视为 0 个标签，低于 min_tags 时触发 issue"""
+        title = "合规标题测试"
+        content = "这是符合要求的内容。" * 50
+        result = engine.validate_content(content, title, "wechat", tags=None)
+
+        tag_issues = [i for i in result["issues"] if i.get("category") == "tag_count"]
+        # 微信 min_tags=3，tags=None 时 tag_count=0 < 3，触发 medium issue
+        assert len(tag_issues) > 0
+        assert tag_issues[0]["severity"] == "medium"
+
 
 # ---------------------------------------------------------------------------
 # ContentFormatter 测试