To fetch a remote Github Pull Request into your local repository so you can test it you need to do the following:
git fetch origin pull/ID/head:BRANCHNAME
ID is the pull request id and
BRANCHNAME is the name of the new branch that you want to create.
Once you have created the branch, then simply check out the branch
git checkout BRANCHNAME
which then allows you to do a npm run dev to do some serious testing.
See the official GitHub documentation for more.
This is ideal when you have created a major pull request or ran a LaravelShift upgrade.
Props Timbo @ https://stackoverflow.com/a/30584951/460885