I never got the name for it. After consulting an AI, I guess it would be Greenfield in what you are doing, while using it as a part of the main process maybe Throwaway Prototyping. Needs a better name, I think. I read it as part of an agile document.

To keep the functions up to spec, Behaviour Driven Development (BDD) would fit well with it because the tests are human-readable. In Java, I've used Cucumber. I read that there is a javascript version.