This is a simple test to illustrate the bug identified in versions of jest >= 21.0.0.
Simply run yarn install and then jest.
You will notice that our test fails with a custom resolver specified in our package.json.
Removing this reference in our package.json and then running jest, you will notice that the tests now pass.
Additionally, downgrading to jest@20.0.4 (the previous version of jest), and running jest with a custom resolver, you will notice that the tests still pass.