anchor.diff:    Future<void> test_argumentList_positional_with_requiredPositional() async {
       await assertContextType('''
   void f(String s, bool b, [int i]) {}
  -void g(int j) {
  -  f('', 3, i:^);
  +void g() {
  +  f('str', false, ^);
   }
   ''', 'int');
     }
  
positive.code:   Future<void> test_argumentList_requiredPositional_last() async {
      await assertContextType('''
  void f(int i, String str, bool b) {}
  void g(int j) {
    f(1, '2', t^);
  }
  ''', 'bool');
    }
  
negative.code:   Future<void> test_argumentList_requiredPositional_last_implicit() async {
      await assertContextType('''
  void f(int i, String str, bool b, num n) {}
  void g() {
    f(1, 'str', ^);
  }
  ''', 'bool');
    }
  