code: def test_no_custom_field():
      dataset = CaptionDataset(100)
  
      with NamedTemporaryFile() as handle:
          writer = DatasetWriter(
              handle.name, {"label": StringField(MAX_STRING_SIZE)}
          )
  
          writer.from_indexed_dataset(dataset)
          with pytest.raises(ValueError):
              Loader(
                  handle.name,
                  batch_size=10,
                  num_workers=2,
                  order=OrderOption.RANDOM,
                  pipelines={"label": [StringDecoder()]},
              )
  
file_path: ffcv/tests/test_custom_field.py
imports: import pytest
  import numpy
  from uuid import uuid4
  from ffcv.fields.ndarray import NDArrayField, NDArrayDecoder
  from ffcv.writer import DatasetWriter
  from ffcv.loader import Loader, OrderOption
  from tempfile import NamedTemporaryFile
label_desc: Use image node_id 2 for calling a global function with example usage: test_no_custom_field() without return types