Use `mount` rendering in tests

Hello,

As a maintainer of the Enzyme adapter for Preact, I would strongly recommend that new code should using the `mount` ("full DOM rendering") rather than the `shallow` rendering mode as this template currently does. I wrote a [blog post](https://robertknight.me.uk/posts/shallow-rendering-revisited/) a while back which explains the rationale in detail and alternative ways to achieve the same results. In brief the main reasons are that shallow rendering tends to lead to brittle tests which are a pain to maintain, and the approach has fallen out of favor in the ecosystem, so there are less resources available related to it.

If I can find time to submit a PR I will do so, but otherwise I'd welcome someone else to make the change.

未指定檔案或測試路徑。找出目前使用 shallow rendering 的範本測試，檢視這些測試的結構，並確認要求的變更涵蓋的案例。相關測試使用 mount rendering 且測試套件通過，即表示完成。

由索引模型根據 Issue 內容生成。