code: def test_repr(self):
      fields = {"x": [1, 2, 3], "y": [4, 5, 6], "z": [1, 1, 1]}
      ins = Instance(**fields)
      # simple print, that is enough.
      print(ins)
  
imports: import os
  import pytest
  import numpy
  from fastNLP.core.dataset import DataSet, FieldArray, Instance, ApplyResultException
  from fastNLP import logger
label_desc: Use image node_id 4 for calling the TestCase obj's underlying member method code with example usage: obj.test_repr() without return types