Rework testing strategy to avoid using manually injected dependencies just for testing purpose

[rpl]

Currently we are adding optional parameters to many of the internal functions just to be able to mock those "dependencies" for testing purpose, it would be better if we could rework the testing strategy to avoid that as much as possible.

This issue goal is to evaluate the alternative approaches (e.g. sinon stubs, and module mocks as the ones supported by Jest).