完善文档

docs/testing/strategy.md

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+# Testing Strategy
+
+测试层次：
+
+```mermaid
+flowchart TB
+    Unit --> Integration
+    Integration --> API
+    API --> Workflow
+    Workflow --> Evaluation
+    Evaluation --> E2E
+```
+
+Agent 系统除了传统测试，还必须建立：
+
+- Agent Evaluation
+- RAG Evaluation
+- Tool Reliability Evaluation