[Side B] Pursuing OSS Quality Assurance with AI: Achieving 369 Tests, 97% Coverage, and GIL-Free Compatibility

From the Author: Recently, I introduced D-MemFS on Reddit. The response was overwhelming, confirming that memory management and file I/O performance are truly universal challenges for developers everywhere. This series is my response to that global interest. 🧭 About this Series: The Two Sides of Development To provide a complete picture of this project, I’ve split each update into two perspectives: Side A (Practical / from Qiita): Implementation details, benchmarks, and technical solutions. Side B (Philosophy / from Zenn): The development war stories, AI-collaboration, and design decisions. Testing is a "Contract between the Design Document and the Code" Why do we write tests? "To prevent bugs," is correct, but I want to phrase it differently. I believe tests are a contract between the design document and the code. In the context of "Spec-First AI Development" that I wrote about in the previous article—a method I later learned is called SDD (Specification Driven Development)—testing i