Implementation of unit tests

[daikikatsuragawa]

I recommend that you implement unit tests. To develop this software effectively and safely. And can be run on Github Actions.

[Ryuno-Ki]

Planned as part of refactoring branch.

https://github.com/nostalgia-dev/nostalgia/blob/335075ee4fb06a372e623d8e8e9bf9e0ca4e5a20/nostalgia/test/TestCase.py