anchor.diff:      messageMatcher.describe(description);
     }
   
  -  Description describeMismatch(item, Description mismatchDescription, MatchState matchState,
  +  Description describeMismatch(item, Description mismatchDescription, Map matchState,
                                  bool verbose) {
  -    var e = matchState.state['exception'];
  +    var e = matchState['exception'];
   
       mismatchDescription.add('threw ').addDescriptionOf(e);
   
  
positive.code: library unittest;
  
  import 'package:unittest/unittest.dart';
  import '../lib/mirrors.dart';
  import 'dart:async';
  
  export 'package:unittest/unittest.dart';
  
negative.code: 
    const NegateMatcher(Matcher matcher) : _matcher = matcher;
  
    bool matches(obj, Map ms) {
      return !_matcher.matches(obj, ms);
    }
  
  