Created by: gaearon
This fixes https://github.com/facebookincubator/create-react-app/issues/2230#issuecomment-302673174 specifically (note: not the same as main issue in #2230 (closed) which was fixed in #2242).
Reproducing code was in https://github.com/ingro/cra-test-bug.
The underlying cause is https://github.com/facebook/jest/pull/3616. However I want to make sure any other tools we use in the future don't have the same problem, and consolidate our cleanup of NODE_PATH (since we already do it for Webpack anyway).