Fail on yarn test with Jest : Cannot find module 'react' from 'Form.js'

I'm starting my first node/react project and I try to write my first tests using Jest.

When I run them using yarn test, it fails with the following message :

Cannot find module 'react' from 'Form.js'

    However, Jest was able to find:
        './App.css'
        './App.js'
        './App.test.js'

    You might want to include a file extension in your import, or update your
 'moduleFileExtensions', which is currently ['web.js', 'js', 'web.ts', 'ts',
'web.tsx', 'tsx', 'json', 'web.jsx', 'jsx', 'node'].

I created my project using create-react-app and here is my package.json :

{
  "name": "client",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^4.2.4",
    "@testing-library/react": "^9.3.2",
    "@testing-library/user-event": "^7.1.2",
    "react": "^16.13.1",
    "react-dom": "^16.13.1",
    "react-router-dom": "^5.2.0",
    "react-scripts": "3.4.1",
    "shards-react": "^1.0.3"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",

    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "proxy": "http://localhost:5000"
}

I don't understand what the Form.js file is, as I didn't create such a File. I guess there is something wrong with my dependencies in package.json but I can't find an explanation for now.