Design Doc- Example Mapping Update

依據12/20會議中定義的 Example Mapping 原則重新撰寫 EM 並更新在 Design-Document.md 文件裡

**given 測試的環境
when 想測的操作
then 預期操作的結果**

> 寫given when then有下列要點
> 1. Given 專注於先決條件
> 2. When 是用來凸顯一個動作
> 3. Then 是一種結果,總是為T/F
> Then可以有多種行為, 如果要寫很多, 用 behave 寫會很煩。
> 視情況直接用 unitest module

Open Design-Document.md and review the existing Example Mapping content against the given/when/then principles listed in the issue. Rewrite the EM examples in that document, using the stated guidance about preconditions, actions, boolean results, and when unit tests may be preferable to behave. Done means the document reflects the updated principles and examples.

Written by the indexing model from the issue text.