JSDom 11.12 causes tests to fail

[iansu]

It looks like the latest version of JSDom is incompatible with one of the default settings in Jest.

Here's the Jest issue: jestjs/jest#6766

This appears to have been fixed but not yet released: jestjs/jest#6792

Even when the fix is released we will still be running an older version of Jest that may not be updated. I think our options for fixing this are:

1. Update to a newer version of Jest (I think there is at least one PR in the works to do this)
2. Add testURL: 'http://localhost' to our Jest config

[iansu]

On further investigation it looks like we already have testURL: 'http://localhost in our Jest config here: https://github.com/facebook/create-react-app/blob/next/packages/react-scripts/scripts/utils/createJestConfig.js#L37

[skoging]

The fix has been released with Jest 23.5 and the PR has been updated: #4846