code: def test_process(self):
      data_bundle = CMRC2018Loader().load("data_for_tests/io/cmrc/")
      pipe = CMRC2018BertPipe()
      data_bundle = pipe.process(data_bundle)
  
      for name, dataset in data_bundle.iter_datasets():
          for ins in dataset:
              if "target_start" in ins:
                  #  抓到的答案是对应上的
                  start_index = ins["target_start"]
                  end_index = ins["target_end"] + 1
                  extract_answer = "".join(
                      ins["raw_chars"][start_index:end_index]
                  )
                  assert extract_answer == ins["answers"][0]
              # 测试context_len是对的
              raw_chars = ins["raw_chars"]
              expect_len = raw_chars.index("[SEP]")
              assert expect_len == ins["context_len"]
  
imports: import pytest
  from fastNLP.io.pipe.qa import CMRC2018BertPipe
  from fastNLP.io.loader.qa import CMRC2018Loader
label_desc: Use image node_id 1 for calling the CMRC2018PipeTest obj's underlying member method code with example usage: obj.test_process() without return types