Add Test Cases

[rcampanate]

Tutorials: https://developers.sap.com/tutorials/add-test-cases.html

There is an error on the test.js (at least for the current version running on the BTP provided on the practice system).
the 3 initial lines
const cds = require('@sap/cds/lib')
const { default: axios } = require('axios')
const { GET, POST, DELETE, PATCH, expect } = cds.test(__dirname + '../../')

should be replace by this:
const cds = require('@sap/cds/lib')
const { GET, POST, DELETE, PATCH, expect, axios } = cds.test(__dirname + '../../')