Code Quality: Introduce unit tests

[0x5bfa]

📄 Description

Add a tests project to FluentHub to test features automatically
This change will require research about integration tests and knowledge on how to implement them properly.

⚡ Required changes

• Add unit tests

✅ Tasks

📋 Checklist:

• Search about integration tests in WinUI
• Add a project for integration tests
• Run the project locally
• Add a task to build and run the project in CI

[Lamparter]

Unit tests are much easier for class libraries. You wanna implement UI tests as well like in Files?

[0x5bfa]

No I mean unit tests for class libraries such as the core.

[Lamparter]

No I mean unit tests for class libraries such as the core.

Oh! Let's do this in #486