Implement unit tests

[Munter]

The current test setup is more of an integration test than an actual unit test. This means testing is vulnerable to all sorts of race conditions, side effects from file indexing when mounting a drive etc.

It would be highly beneficial to split out some of the actual computation from the mounted file system part of the code to better guarantee stability in those parts.

Hopefully this will also make the integration testing part easier, as fewer moving parts will have to be tested on a brittle setup

[jackfranklin]

Definitely up for taking a stab at this 👍 Will hopefully find some time soon to read through the code before thinking about how to split it up :)