Testing strategy

[wovalle]

Once #19 is merged, we'll have an overview of the app as a whole. I think we can start implementing (or designing) a test strategy.

I think we can't start testing services and then move to logic in components. I wouldn't think of e2e so soon, I would test our core logic instead.

Note: this is a long running issue, that is thought to open the discussion on this matter. Once discussed, individual tasks should have issues on their own.