Small NodeJS code with mocha/chai to test replacing each char in a string with the next char in alphabet

Steps to install and execute the tests:

1. Install node.js npm install --save -dev

2. Initialize project npm init

3. Install mocha and chai dependencies npm install mocha --save -include=dev

npm install chai --save -include=dev

4. Modify package.json

"scripts": {
    "test": "mocha"
  }

5. To execute the test cases, the following instruction is executed in terminal: npm test