anchor.diff:            return storage.addAll(_validValues);
           })
           .then((_) {
  -          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]);
  -                });
  -          });
  +          return _matchesValidValues(storage);
           });
     });
   
  
positive.code:   });
  
    test('store pnp', () {
      return Future
          .forEach(PNP.keys, (String chapter) {
        return storage.set(chapter, PNP[chapter]);
          })
          .then((_) {
            return storage.getKeys();
          })
  
negative.code:   });
  
    test('add many and clear', () {
      return storage.addAll(_validValues)
      .then((_) {
        return _matchesValidValues(storage);
      })
      .then((_) {
        return storage.clear();
  