title: Jest fails on anythings: path must be a string. Received undefined
body: <p>I have the same problem as <a href="https://stackoverflow.com/questions/46220674/jest-typeerror-path-must-be-a-string-received-undefined">this "duplicate" question</a>. I made an empty project and installed only jest. Then I created one sample test file. When I run jest, it gives an error: </p>
  
  <pre><code> FAIL  __tests__/test.test.js
  ● Test suite failed to run
  
  TypeError: Path must be a string. Received undefined
  
    at assertPath (path.js:28:11)
    at Object.relative (path.js:1254:5)
  </code></pre>
  
  <p>I have the latest version of npm, and the jest version is 21.2.1. Mac.
  Any ideas what might be causing it?</p>
  
  <p>EDIT: version 20.0.4 works just fine, so I go with it for now. </p>