Add BE tests
Starting to add test to the BE
NOTE:
Node18 has been released and it introduces test runner natively, so it's not necessary to install anything else -> https://nodejs.org/api/test.html
Moreover, it looks like Jest is probably reaching its end since recently Facebook is transferring it and only one person (not paid) is working on it -> https://engineering.fb.com/2022/05/11/open-source/jest-openjs-foundation/