title: Jest pattern "" - 0 matches (moving from jest 19 -> jest 20)
body: <p>I'm using the following jest.unittest.json file (used via jest --config option):</p>
  
  <pre><code>{
    "bail": false,
    "verbose": true,
    "transform": {
      "^.+\\.(ts|tsx)$": "typescript-babel-jest"
    },
    "testPathIgnorePatterns": [
      "&lt;rootDir&gt;/lib",
      "&lt;rootDir&gt;/lib_es6",
      "/node_modules/",
      "fixtures.ts",
      "/fixtures/"
    ],
    "moduleFileExtensions": [
      "js", "jsx", "ts", "tsx", "node"
    ],
    "roots": [
      "&lt;rootDir&gt;/src/__unittests__/Logger",
      "&lt;rootDir&gt;/src/__unittests__/Renderer/renderer.test.ts"
    ],
    "testRegex": "&lt;rootDir&gt;/src/__unittests__/.*\\.test.(ts|tsx|js|jsx)$"
  }
  </code></pre>
  
  <p>Note the test files are src/<strong>unittests</strong>/Renderer/renderer.test.ts, and so on.</p>
  
  <p>It used to work until jest v19, but after upgrading to v20, this config no longer works.</p>
  
  <p>When I do jest --config jest.unittest.json --verbose, I get:</p>
  
  <p><code>Pattern: "" - 0 matches</code></p>
  
  <p>Is there anything wrong with my config?</p>