anchor.diff:          });
       });
   
  -
  -
       test('change not existing data. (T05)', () {
         // when
         Future shouldThrow =  ready.then((_) => months.change('january', new Map.from(february), 'Michael Smith'));
  
positive.code: 
      tearDown(() {
        mongodb.close();
  
      });
  
      test('get data. (T01)', () {
        // when
        return ready.then((_) {
          // then
          return months.data().then((Map data) {
            expect(data['data'], equals([]));
  
negative.code:           expect(diff['version'], equals(2));
            expect(diff['author'], equals('Michael Smith'));
          });
      });
  
      test('remove non-existing data. (T08)', () {
        // when
        Future shouldNotThrow =ready.then((_) => months.remove('january', 'Michael Smith'));
  
        // then
          expect(shouldNotThrow, completion(isTrue));
      });
  
      test('can reconstruct changes form diff. (T09)', () {
  