title: Why Code Coverage in react app is empty? Tried using npm run test -- --coverage. But always showing empty code coverage
body: <p>I need help to find code coverage.</p>
  <p>I have just created a new app using the latest create-react-app.</p>
  <p>I am trying to find the code coverage using <code>npm run test -- --coverage</code>. this is showing empty code coverage. Can any please help me to find where I am missing.</p>
  <pre><code> PASS  src/__tests__/App.test.js
    ✓ renders without crashing (2ms)
  
  ----------|----------|----------|----------|----------|-------------------|
  File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
  ----------|----------|----------|----------|----------|-------------------|
  All files |        0 |        0 |        0 |        0 |                   |
  ----------|----------|----------|----------|----------|-------------------|
  Test Suites: 1 passed, 1 total
  Tests:       1 passed, 1 total
  Snapshots:   0 total
  Time:        0.17s, estimated 1s
  Ran all test suites.
  
  Watch Usage: Press w to show more.
  </code></pre>