anchor.diff:    });
   
     test('add many and clear', () {
  -    return Future.forEach(_validValues.keys, (key) {
  -      return storage.set(key, _validValues[key]);
  -    })
  +    return storage.addAll(_validValues)
       .then((_) {
  -      return Future.forEach(_validValues.keys, (key) {
  -        return storage.get(key)
  -            .then((value) {
  -              expect(value, _validValues[key]);
  -            });
  -      });
  +      return _matchesValidValues(storage);
       })
       .then((_) {
         return storage.clear();
  
positive.code:   });
  }
  
  const _validValues = const {
    'null': null,
    'string': 'a string',
  
negative.code:           return storage.addAll(_validValues);
          })
          .then((_) {
            return _matchesValidValues(storage);
          });
    });
  
  