code: def test_init(self):
      fields = {"x": [1, 2, 3], "y": [4, 5, 6]}
      ins = Instance(x=[1, 2, 3], y=[4, 5, 6])
      assert isinstance(ins.fields, dict) == True
      assert ins.fields == fields
  
      ins = Instance(**fields)
      assert ins.fields == fields
  
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 1 for calling the TestCase obj's underlying member method code with example usage: obj.test_init() without return types