Add tests/ テストを追加する

[meganetaaan]

Is your feature request related to a problem? Please describe.

As the number of modules increases it is likely to find more regression, especially the variation of the same base class.

モジュールの数が増えるにつれて、特に同じベースクラスを持つ複数のクラス間でリグレッション（今まで動いていた機能が改修によって壊れること）が増えてきました。

Describe the solution you'd like

Add automated unit tests. Better if they are triggered by GitHub Actions.　

自動単体テストを追加します。GitHub Actionsでトリガーできるとなお良いです。

[meganetaaan]

I should read the official testing doc first.

[meganetaaan]

Wow, I didn't know that testmc supports graphics tests

https://github.com/Moddable-OpenSource/moddable/blob/public/documentation/tools/testing.md#graphics-tests

This definitely helps to test avatar rendering features.

[meganetaaan]

[meganetaaan]

We can use self-hosted runners to run hardware tests automatically and locally.

https://github.com/actions/runner