anchor.diff:        };
         _expectParseThrows(monoYaml, r'''
   line 6, column 5: `stages` expects a list of maps with exactly one key (the name of the stage), but no items exist.
  -    {}
  -    ^^''');
  +  ╷
  +6 │     {}
  +  │     ^^
  +  ╵''');
       });
   
       test('null stage job', () {
  
positive.code:       };
        _expectParseThrows(monoYaml, r'''
  line 7, column 7: Stages are required to have at least one job. "a" is null.
        "a": null
        ^^^''');
      });
  
      test('unsupported keys', () {
  
negative.code: 
        _expectParseThrows(monoYaml, r'''
  line 9, column 11: Must have one key of `dartfmt`, `dartanalyzer`, `test`, `command`.
    ╷
  9 │           "weird": "thing"
    │           ^^^^^^^
    ╵''');
      });
  
      test('Stage tasks entries must have one key in the approved set', () {
  