Run jest to see the issue:
$ jest
Using Jest CLI v0.2.1
FAIL __tests__/Authenticator.js
TypeError: /Users/ben/projects/jest-issue/__tests__/Authenticator.js: /Users/ben/projects/jest-issue/lib/Authenticator.js: /Users/ben/projects/jest-issue/node_modules/body-parser/index.js: Cannot call method 'function' of undefined
1 test failed, 0 tests passed (1 total)
Run time: 0.311s