code: def test_fillna_no_op_returns_copy(self, data):
      data = data[~data.isna()]
  
      valid = data[0]
      result = data.fillna(valid)
      assert result is not data
      tm.assert_extension_array_equal(result, data)
  
      result = data.fillna(method="backfill")
      assert result is not data
      tm.assert_extension_array_equal(result, data)
  
imports: from __future__ import annotations
  import string
  from typing import cast
  import numpy
  import pytest
  import pandas
  import pandas._testing
  from pandas.api.types import is_string_dtype
  from pandas.core.arrays import ArrowStringArray
  from pandas.core.arrays.string_ import StringDtype
  from pandas.tests.extension import base
label_desc: Use image node_id 8 for calling the TestStringArray obj's underlying member method code with example usage: obj.test_fillna_no_op_returns_copy(data) without return types