I gave a short talk about REST API design on Saturday, February 23rd, 2019.
It was about common mistakes which are made when one is designing REST API. I have experience with most of them and I tried to describe how to solve them.
For example, good test for your API can be simple SPA (Single Page Application), where you'll see the reality. You can try create-react-app for that.
I also mentioned HATEOAS at the end, which can help "machines" to navigate in your API response (and what to follow). Also it can be useful for automated UI generation.