test: Coverage for repository

[mfw78]

Problem
As we build on top of the repository layer that we wrote, it is critical that this layer performs as expected.

Solution
Unit tests to cover basic functionality, but particularly, we require:

• Testing all getters to make sure that they return a consistent value (suggest type | null).
• Testing of all indices to make sure that they are being managed correctly (add a stub, adds it to the indices., remove a stub, removes from the indices).