Add mock code and unit tests to guarantee the stability of the API

Dear all,

I believe we should begin adding more mock code and unit tests to guarantee the stability of the API in the future while working our way up to v1.0.0.

Creating mock classes for the whole API should be a community effort, since it is tedious work that involves a lot of boilerplate code. What we get in return, however, will be a way to automatically check for any break in the API, especially when we set up the CI for this project. Additionally, consumers can use the mock code to implement the API.

I will provide a draft PR to start the discussion on how we could approach this.

I know that work has been started e.g. in test_utils.h, but as of now it is incomplete.

Cheers, Martin

Martin Stump martin.stump@mercedes-benz.com on behalf of Mercedes-Benz Tech Innovation GmbH, Provider Information