title: Can You Place a Debug Breakpoint for System Functions in PHPUnit/XDebug?
body: <p>In PHPUnit, I would like to put a breakpoint for a built-in function. Is this possible and how?</p>
  
  <p>For example, I would like to break everytime <code>ob_end_clean</code>.</p>
  
  <p>Thanks.</p>