Issue
When running a build with the Node buildpack, the build errors with yarn: not found.
Resolution
Users will see a yarn: not found later in the script if there is a script that calls yarn.
The Node.js buildpack looks for a yarn.lock file to determine whether it will install yarn. If the yarn.lock has not been committed, has been deleted, or is in the .gitignore, the buildpack will not install yarn.
Make sure to commit yarn.lock files for every package.json, and do not leave them in the .gitignore.