title: Jest watch with code coverage not working
body: <p>I'm trying to run <code>jest --coverage --watch</code> so that I only get the coverage for whatever component I'm writing tests for and I can see the increased coverage as I write more tests. But while the modified tests are successfully picked up and run, the coverage report comes up empty.</p>
  
  <pre><code>----------|----------|----------|----------|----------|-------------------|
  File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
  ----------|----------|----------|----------|----------|-------------------|
  All files |        0 |        0 |        0 |        0 |                   |
  ----------|----------|----------|----------|----------|-------------------|
  
  
  Test Suites: 2 passed, 2 total
  Tests:       2 passed, 2 total
  Snapshots:   0 total
  Time:        5.599s
  Ran all test suites related to changed files.
  </code></pre>
  
  <p>The documentation on this is almost zero, but it seems like it should work according to this pr: <a href="https://github.com/facebook/jest/pull/5601" rel="nofollow noreferrer">https://github.com/facebook/jest/pull/5601</a></p>