anchor.diff:    }
   }
   
  -class ComplexExceptionMatcher extends BaseMatcher {
  +class ComplexExceptionMatcher extends Matcher {
     Matcher classMatcher;
     Matcher messageMatcher;
   
  
positive.code: Matcher not(Matcher matcher) => new NegateMatcher(matcher);
  
  
  class NegateMatcher extends BaseMatcher {
    final Matcher _matcher;
  
    const NegateMatcher(Matcher matcher) : _matcher = matcher;
  
negative.code:   }
  }
  
  class IsInstanceOfTypeMatcher extends Matcher {
    Type t;
  
    IsInstanceOfTypeMatcher(Type t) {
  