Unit testing for the Business logic (the store and webxdc state update processing)

[Simon-Laux]

The heart of the app is the store at src/store.ts, it emits and processes all webxdc state updates and builds and application state from them.

What it should do is clear, so it would make sense to create unit tests for everything it should do to ensure it stays working with future changes.

We already have unit tests for some utility functions (src/entryMaths.ts) so that could be used as example on how to add such tests. The tests for it are in src/entryMaths.spec.ts.