Explore Unittest possibillities

[Snapstromegon]

This is mainly for myself.

Since people actually want to use this, I want to provide more assurances than "it feels right". Because of that I want to explore the possible options for unittesting this.

A solution should:

• work mostly without writing to disk (good for performance)
• be easy to use
• allow for easy expansion

I will probably go for ava since I already know it and it's also used in 11ty.