anchor.diff:      ]);
     }
   
  -  test_index_null() async {
  -    await assertErrorsInCode(r'''
  -f(Null x) {
  -  x[0];
  -}
  -''', [
  -      error(CompileTimeErrorCode.UNDEFINED_OPERATOR, 15, 3),
  -    ]);
  -  }
  -
     test_index_set_extendedHasGetter_extensionHasSetter() async {
       await assertErrorsInCode(r'''
   class A {
  
positive.code: const B = ~((1 << A) - 1);
  ''');
    }
  
    test_unaryMinus_null() async {
      await assertErrorsInCode(r'''
  m() {
    Null x;
    -x;
  
negative.code:     ]);
    }
  
    test_prefixExpression_mixin() async {
      await assertErrorsInCode(r'''
  mixin M {}
  