anchor.diff:  // We use a 'dummy' context for the top level to eliminate null
   // checks when querying the context. This allows us to easily
   //  support top-level setUp/tearDown functions as well.
  -GroupContext _rootContext = new GroupContext();
  -GroupContext _currentContext = _rootContext;
  +final _rootContext = new _GroupContext();
  +_GroupContext _currentContext = _rootContext;
   
   int _currentTestCaseIndex = 0;
   
  
positive.code:       ? _name
        : "${parent.fullName}$groupSep$_name";
  
    GroupContext([this.parent, this._name = '']) {
      _testSetup = parentSetup;
      _testTeardown = parentTeardown;
    }
  
negative.code:  * Setup and teardown functions for a group and its parents, the latter
   * for chaining.
   */
  class _GroupContext {
    final _GroupContext parent;
  
    /** Description text of the current test group. */
    final String _name;
  