If you wish to test the Contacts Book UI app on your local machine, please install dependencies by running npm i command from the root folder.
Then use npm start command to run the application in development mode or npm run build command to build a shippable folder of static files.
In the latter case you may serve it with a static server package:
npm install -g serve serve -s build
Due to limited time that has been assigned to this exercise, I did not use TDD for this project. However, when writing unit tests, I always follow a very concrete convention and in order to present this, I have added one suite validator.test.js I am happy to write more unit tests upon request, to prove the ability and present different approaches to test React components.
To run unit tests, please use npm test command at the root folder level.