e2e tests incorrectly caching react-scripts

[ro-savage]

This caused me a lot of grief and many many hours of lost time on PR #2285.

Yarn is caching old react-scripts when running the e2e tests, which means old versions are being used during the build process. Fine for CI where each build is on a clean machine but breaks e2e in unforeseen ways on local machines.

This might be related to yarnpkg/yarn/issues/2165

The fix was to yarn clean cache before running the e2e tests.

One possible solution would be to add

if hash yarnpkg 2>/dev/null
then
  yarn cache clean
fi

if hash npm 2>/dev/null
then
  npm cache clean
fi

to each of the bash scripts.

Another would be to install using the yarn install --force which will refetch all the packages. However I think that the install part is coming from within react-scripts and therefore it would force everyone to install with --force. I couldn't see an install command inside the bash scripts.

Reproduction

• Clone the create-react-app repo.
• npm install
• Run tasks/e2e-kitchensink.sh.
• Open e2e-kitchensink.sh and remove the line rm -rf "$temp_cli_path" "$temp_app_path" "$temp_module_path" || $CI so that you can keep the folders.
• Edit the description in packages/react-scripts/package.json.
• Re-run `tasks/e2e-kitchensink.sh.
• Find the tmp folder the project is made into on the command line
• cd to the tmp folder
• open up the package.json found in test-kitchensink/node_modules/react-scripts
• Check the description and see it hasn't changed.

This causes issues because when running e2e-kitchensink.sh is builds a CRA in a tmp folder. It then runs npm test internally in this folder.
This runs react-scripts test --env=jsdom which looks up it's node_modules to find react-scripts so that it can run scripts/test.js. Which is old one, meaning if you edited this file or other related files the e2e will be running the cached version not the newly modified version.