create react app in an already existing project that was made using create react app

I have an existing project that was made using create react app and i want to make a new test folder using create react app so it will have a package.json file inside it that will configure a jest/enzyme test suite. Is this possible and will the test suite take the local package.json and node_modules. Is this legal to do and will it let me customize the package.json file for the test suite only?