anchor.diff:    Future<void> test_argumentList_requiredPositional_middle() async {
       await assertContextType('''
   void f(int i, String str, bool b) {}
  -void g(int j) {
  +void g() {
     f(1, w^);
   }
   ''', 'String');
  
positive.code:   Future<void> test_argumentList_requiredPositional_middle_implicit() async {
      await assertContextType('''
  void f(int i, String str, bool b) {}
  void g(int j) {
    f(1, ^ );
  }
  ''', 'String');
  
negative.code:   Future<void> test_argumentList_positional_with_requiredPositional() async {
      await assertContextType('''
  void f(String s, bool b, [int i]) {}
  void g() {
    f('str', false, ^);
  }
  ''', 'int');
    }
  