anchor.diff:  
       observeTest('removeRange', () {
         list.removeRange(1, 4);
  -      expect(list, orderedEquals([1, 3, 4]));
  +      expect(rol, orderedEquals([1, 3, 4]));
   
         performMicrotaskCheckpoint();
         expectChanges(records, [
  
positive.code: 
      observeTest('clear', () {
        list.clear();
        expect(list, []);
  
        performMicrotaskCheckpoint();
        expectChanges(records, [
  
negative.code:     observeTest('set multiple times results in one change', () {
        list[1] = 777;
        list[1] = 42;
        expect(rol, [1, 42, 3]);
        performMicrotaskCheckpoint();
        expectChanges(changes, [
          _change(1, addedCount: 1, removedCount: 1),
  