anchor.diff:    });
   
     test('store pnp', () {
  -    return Future
  -        .forEach(PNP.keys, (String chapter) {
  -      return storage.set(chapter, PNP[chapter]);
  -        })
  +      return storage.addAll(PNP)
           .then((_) {
             return storage.getKeys();
           })
  
positive.code:   });
  
    test('add many and clear', () {
      return Future.forEach(_validValues.keys, (key) {
        return storage.set(key, _validValues[key]);
      })
      .then((_) {
        return Future.forEach(_validValues.keys, (key) {
          return storage.get(key)
              .then((value) {
                expect(value, _validValues[key]);
              });
        });
      })
      .then((_) {
        return storage.clear();
  
negative.code:   });
  }
  
  Future _matchesValidValues(Storage storage) {
    return storage.getKeys()
      .then((List<String> keys) {
        expect(keys, unorderedEquals(_validValues.keys));
  
        return Future.forEach(keys, (k) {
          return storage.get(k)
              .then((dynamic value) {
                expect(value, _validValues[k]);
              });
        });
      });
  }
  
  const _validValues = const {
    'null': null,
    'string': 'a string',
  