code: def test_data_processor():
      x = 5
      data_processor_empty = DataProcessor()
      assert not data_processor_empty._preprocess_fn
      assert not data_processor_empty._postprocess_fn
  
      with pytest.raises(UserWarning):
          data_processor_empty.preprocess(x)
  
      with pytest.raises(UserWarning):
          data_processor_empty.postprocess(x)
  
      data_processor = DataProcessor(
          preprocess_fn=dummy_preprocess,
          postprocess_fn=dummy_postprocess,
      )
  
      x = data_processor.preprocess(x)
      x = data_processor.postprocess(x)
      assert x == 5
  
      data_processor_empty.set_preprocess_fn(dummy_preprocess)
      data_processor_empty.set_postprocess_fn(dummy_postprocess)
  
      x = data_processor_empty.preprocess(x)
      x = data_processor_empty.postprocess(x)
      assert x == 5
  
imports: import pytest
  from chitra.data_processing import DataProcessor, batchify
label_desc: Use image node_id 3 for calling a global function with example usage: test_data_processor() without return types