anchor.diff:  
   test1() {
     Map data = {'A': 10, 'B': 20, 'C': 30};
  -  List res = flattenMap(data);
  +  List res = flattenMap(data, ['level0', 'value']);
     //res.forEach(print);
     test('flattenMap, one nesting level', () {
       expect(res, [
  
positive.code:       {'level0': 'B3', 'level1': 'Feb15', 'value': 6},
      ]);
    });
  }
  
  test3() {
    Map data = {
  
negative.code:     'B2': {'Jan15': 3, 'Feb15': 4},
      'B3': {'Jan15': 5, 'Feb15': 6}
    };
  
    //res.forEach(print);
    test('flattenMap, two nesting levels', () {
      List res = flattenMap(data, ['level0', 'level1', 'value']);
      expect(res, [
        {'level0': 'B1', 'level1': 'Jan15', 'value': 1},
        {'level0': 'B1', 'level1': 'Feb15', 'value': 2},
  