anchor.diff:    }
   
     Token parseFactoryMethod(Token token) {
  +    assert(isFactoryDeclaration(token));
       firstToken ??= token;
  -    assert(isFactoryDeclaration(token));
       Token start = token;
       bool isExternal = false;
       int modifierCount = 0;
  
positive.code:         identical(value3, stringValue);
    }
  
    /// Returns true if the stringValue of the [token] is either [value1],
    /// [value2], [value3], or [value4].
    bool isOneOf4(
        Token token, String value1, String value2, String value3, String value4) {
  
negative.code: 
    Token parseOptionalFormalParameters(
        Token token, bool isNamed, MemberKind kind) {
      assert((isNamed && optional('{', token)) || optional('[', token));
      Token begin = token;
      listener.beginOptionalFormalParameters(begin);
      int parameterCount = 0;
      do {
        token = token.next;
  