title: Code coverage "Unknown" using jest 15.1.1
body: <p>When I try to include all the project source code to get a more reasonable code coverage figure, I end up with</p>
  
  <pre><code>----------|----------|----------|----------|----------|----------------|
  File      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
  ----------|----------|----------|----------|----------|----------------|
  All files |  Unknown |  Unknown |  Unknown |  Unknown |                |
  ----------|----------|----------|----------|----------|----------------|
  </code></pre>
  
  <p>My config contains the following:</p>
  
  <pre><code>"collectCoverageFrom": [
      "&lt;rootDir&gt;/app_modules/",
      "&lt;rootDir&gt;/src/"
  ],    
  </code></pre>
  
  <p>I've also tried it without the trailing <code>/</code>, with <code>**/*.js</code> and with just a trailing <code>*.js</code> all to no avail.</p>
  
  <p>Based on the <code>--debug</code> option, the path expands to the paths I want to collect coverage information from ( isn't the problem)</p>
  
  <p>So what is the magic to getting more accurate coverage information?</p>
  
  <p>The best docs I've been able to find come from this Github PR:  <a href="https://github.com/facebook/jest/pull/1349/files" rel="noreferrer">https://github.com/facebook/jest/pull/1349/files</a></p>
  
  <hr>
  
  <p>I ended up doing:</p>
  
  <pre><code>"collectCoverageFrom": [
      "**/*.js",
      "!webpack.config.js"
  ],
  </code></pre>
  
  <p>which only worked because this is part of the default config</p>
  
  <pre><code>"testPathIgnorePatterns": [
      "/node_modules/"
  ],
  </code></pre>
  
  <p>It does add a huge amount of time to the test run though.</p>