Running only subsets of tests

Because I edited my package.json like this…

"scripts": {
    "test": "jest",
    "test:char": "jest --watchAll --testPathPattern=src/character-copier",
    "test:fizzbuzz": "jest --watchAll --testPathPattern=src/fizzbuzz"

… I can run this in the terminal - npm run test:char - and it will watch my code and run tests in the background, but only for the specified folder.

Troubleshooting with React

Invalid hook

  • When you get an error saying invalid hook in jest tests:
  • you might need to update your version of jest
    • like this: npm install react-router-dom@6
  • https://reactjs.org/link/invalid-hook-call
  • https://github.com/next-page-tester/next-page-tester/issues/147

testing-library issues

“Cannot find module ‘@testing-library/react’ from [path to test file]”

  • Solution: npm install --save-dev @testing-library/react
  • or npm install --save @testing-library/react @testing-library/jest-dom

Can’t install testing library because dependencies

ERESOLVE unable to resolve dependency tree npm ERR! npm ERR! While resolving: client@0.1.0 npm ERR! Found: react@17.0.2 npm ERR! node_modules/react npm ERR! react@”^17.0.2” from the root project

This is because you have an old version of react

Solution: npm install react react-dom to get latest version

Upgrading react has no impact

package.json still has "react": "^17.0.2", even after running npm install react react-dom


  • Run the install command in the ROOT of your project (one level higher than client and server)
  • Remove the older react and react-dom versions from dependencies in package.son in the sub-project
  • Run npm install again (in the sub-folder)