title: Use \PHPUnit_Framework_TestCase or ..\TestCase
body: <p>Stupid question...  In the Symfony docs, unit test classes extend <code>\PHPUnit_Framework_TestCase</code> but in PHPUnit docs, test classes extend <code>PHPUnit\Framework\TestCase</code>.  Is there a difference, are they the same, or am I missing a subtle PHP feature where <code>_</code> is equivalent to <code>\</code>?</p>
  
  <p>Short of actually testing it out myself, can I use either, or just one in Symfony?</p>
  
  <p><strong>Update</strong>:  It's been helpfully explained to me that these two classes are just a difference between PHPUnit versions.  After my own research and for the record, Symfony 3.1 still extends <code>\PHPUnit_Framework_TestCase</code> in its own <code>KernelTestCase</code> class that powers Symfony's functional testing.  To avoid breaking code, I'm going to play safe &amp; extend <code>WebTestCase</code> that inherits from <code>\PHPUnit_Framework_TestCase</code> when unit testing with Symfony specifically. Such unit tests still work with PHPUnit 5.6 anyway</p>