anchor.diff:  
         _expectParseThrows(monoYaml, r'''
   line 10, column 11: Must have one and only one key of `dartfmt`, `dartanalyzer`, `test`, `command`.
  -          "command": "other thing"
  -          ^^^^^^^^^''');
  +  ╷
  +10│           "command": "other thing"
  +  │           ^^^^^^^^^
  +  ╵''');
       });
   
       test('empty stage job', () {
  
positive.code:       _expectParseThrows(monoYaml, r'''
  Unrecognized keys: [extra, more]; supported keys: [dart, stages, cache]
  line 2, column 3: Unrecognized key "extra"
    "extra": "foo",
    ^^^^^^^
  line 18, column 3: Unrecognized key "more"
    "more": null
    ^^^^^^''');
      });
  
      test('Duplicate stage names are not allowed', () {
  
negative.code:       };
        _expectParseThrows(monoYaml, r'''
  line 7, column 7: Stages are required to have at least one job. "a" is null.
    ╷
  7 │       "a": null
    │       ^^^
    ╵''');
      });
  
      test('unsupported keys', () {
  