title: Eclipse and PHPUnit: "The import PHPUnit\Framework\TestCase cannot be resolved"
body: <p>I'm starting with PHPUnit, and it works fine so far. I just got one problem:
  Eclipse (Oxygen.3) is telling me in this line:</p>
  
  <pre><code>use PHPUnit\Framework\TestCase;
  </code></pre>
  
  <p>"The import PHPUnit\Framework\TestCase cannot be resolved"</p>
  
  <p>I went to Window -> Preferences -> PHP -> Tools -> PHPUnit and added the path to my phpunit.phar. But this didn't help.</p>
  
  <p>I went to Window -> Preferences -> PHP -> Source Paths -> Libraries and tried to import my phpunit.phar. But this results in an error "The selected file is not a valid user library data file".</p>
  
  <p>Any other ideas how to get rid of this error?</p>