anchor.diff:   * in that it removes the tests completely.
    */
   void filterTests(testFilter) {
  -  var filterFunction;
  +  _requireNotRunning();
  +  Function filterFunction;
     if (testFilter is String) {
       RegExp re = new RegExp(testFilter);
       filterFunction = (t) => re.hasMatch(t.description);
  
positive.code:   final int minExpectedCalls;
    final int maxExpectedCalls;
    final Function isDone;
    final int testNum;
    final String id;
    int actualCalls = 0;
    TestCase testCase;
    bool complete;
    static const sentinel = const _Sentinel();
  
  
negative.code:             return callback();
            }
          },
          after, testCase);
    }
  
    invoke1(arg1) {
  