apache/beam · error · TypeError

f' of test specification must be a list, got

Error message

f'{attr_type} {ix} of test specification {identifier} must be a list, got {type(attr_item["elements"])}'

What it means

The 'elements' field of a test-spec entry is present but is not a list. Elements must be a sequence of row values (mappings or scalars); this guard fires when it was parsed as a scalar or mapping, and reports the actual type of attr_item['elements'].

Solutions

1. Wrap the element rows in a list: elements: [{col: val}, ...]
2. Fix YAML indentation so each element is a list item under 'elements'

When it happens

Trigger: Thrown at sdks/python/apache_beam/yaml/yaml_testing.py:196 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/96de510584d119c6. Report an issue: GitHub.

Appendix: source

Thrown at sdks/python/apache_beam/yaml/yaml_testing.py:196

    if not isinstance(attr, list):
      raise TypeError(
          f'{attr_type} of test specification {identifier} '
          f'must be a list, got {type(attr_type)}')
    for ix, attr_item in enumerate(attr):
      if not isinstance(attr_item, dict):
        raise TypeError(
            f'{attr_type} {ix} of test specification {identifier} '
            f'must be an object, got {type(attr_item)}')
      if 'name' not in attr_item:
        raise TypeError(
            f'{attr_type} {ix} of test specification {identifier} '
            f'missing a name')
      if 'elements' not in attr_item:
        raise TypeError(
            f'{attr_type} {ix} of test specification {identifier} '
            f'missing a elements')
      if not isinstance(attr_item['elements'], list):
        raise TypeError(
            f'{attr_type} {ix} of test specification {identifier} '
            f'must be a list, got {type(attr_item["elements"])}')


def inject_test_tranforms(spec, test_spec, fix_failures):
  validate_test_spec(test_spec)
  scope = yaml_transform.LightweightScope(spec['transforms'])

  mocked_inputs_by_id = {
      scope.get_transform_id(mock_input['name']): mock_input
      for mock_input in test_spec.get('mock_inputs', [])
  }

  mocked_outputs_by_id = _composite_key_to_nested({
      scope.get_transform_id_and_output_name(mock_output['name']): mock_output
      for mock_output in test_spec.get('mock_outputs', [])
  })

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