title: React component testing with Jest
body: <p>I want to test my components using jest, but when I run it i am getting 
  `Cannot find module 'react-router/Router' from 'Router.js'</p>
  
  <pre><code>  at Resolver.resolveModule (node_modules/jest-resolve/build/index.js:191:17)
    at Object.&lt;anonymous&gt; (node_modules/react-router-dom/Router.js:5:15)`
  </code></pre>
  
  <p>if I start development server my application is working corectly. </p>
  
  <p>My jest config in package.json looks like:</p>
  
  <pre><code> "jest": {
      "testPathIgnorePatterns": [
        "/node_modules/"
      ],
      "moduleDirectories": [
        "&lt;rootDir&gt;/node_modules",
        "&lt;rootDir&gt;/src"
      ]
    }
  </code></pre>