Yes, I thought using types could help to understand the interfaces! In the end, TypeScript is a superset of JavaScript, and by removing the return types and the parameter types, you have a clean JavaScript at the end! The concept is the same using Vanilla JavaScript or TypeScript.

Hi Albert Oliva Roura , Thanks. To validate the JSON or you can use the expect directly, like in my example; you can find more on the jest documentation Or you can build your own validation using other libraries like zod, typebox or fluent-json-schema. The official way is by the expect, but I understand is not so simple.

Hi Willy De la Cruz Sierra , thanks for your feedback. I know the doc is not extensive at this moment, unfortunately. I tried to create new examples in this branch , so please take a look there. In a nutshell, the idea is to create small functions that return or do something. Then you can expose them directly as your base test function, or you can create a new one on each test file in base on your tests. For instance, you can create a reusable fixture, if this fixture is required in most of the tests, or create a specific one if the fixture is just for one or two tests in the same file. Let me know if the examples are clear; in case, I'll try to be more exhaustive.