Refactor Tests to a Dedicated `tests/` Folder.

Currently, the codebase does not have a dedicated ```tests/``` folder. All the tests are included within the main code itself. We may consider refactoring to move the tests into a separate folder for better structure and maintainability. What do you think ? @dbieber

未指定檔案或測試進入點。先檢視儲存庫，以找出嵌入主要程式碼中的測試，以及現有測試套件的執行方式。在移動任何內容之前，先確立預期的 tests/ 配置，並維持等效的測試涵蓋率；當測試完成分離且未破壞測試套件時，即表示完成。

由索引模型根據 Issue 內容生成。