anchor.diff:        Set y = mmap['k1'];
         mmap['k1'].add('v0');
         x.add('v1');
  -      y.addAll(['v2', 'v3']);
  +      y.addAll(<String>['v2', 'v3']);
         expect(mmap['k1'], unorderedEquals(['v0', 'v1', 'v2', 'v3']));
       });
     });
  
positive.code: 
      test('addAll(Map m) should throw UnsupportedError', () {
        expect(
            () => map.addAll({
                  'k1': ['1', '2', '3']
                }),
            throwsUnsupportedError);
  
negative.code:       var map = new ListMultimap<String, String>();
        List values1 = map['k1'];
        List values2 = map['k1'];
        values1.addAll(<String>['v1', 'v2']);
        expect(map['k1'], ['v1', 'v2']);
        expect(values2, ['v1', 'v2']);
      });
  