How to fix error after installing jest?

Question

React

Hello. In the create-react-app application, I set in package.json:
npm install --save-dev jest
and then I run the command:
npm run start
This is the error. Can you please tell me how to resolve this error?

Answer 1

You now have 2 files: package-lock.json and yarn.lock. There must be one. Most likely yarn.lock, because react projects prefer yarn.
You need to:
1. Remove jest from devDependencies
2. Remove package-lock.json
3. Run `yarn add -D jest` in order to add jest in the way that create-react-app expects you to.
Actually, this is exactly what is written in message that is displayed when the application starts.