Add API unit testing

I tried to achieve unit testing of my custom endpoints based on :
- https://torquemag.io/2017/01/testing-api-endpoints/

But it is a failure for now. Would be fine to be able to test them by creating and updating resources of certain container types and get them, update them, etc...

Start by reproducing the failed custom-endpoint unit-testing approach described in the issue's TorqueMag article. Inspect how custom endpoints expose resource creation, updating, retrieval, and container types. Done means tests can create and update the relevant resources and retrieve them through the API.

Written by the indexing model from the issue text.