code: def test_iadd_string(self):
      index = pd.Index(["a", "b", "c"])
      # doesn't fail test unless there is a check before `+=`
      assert "a" in index
  
      index += "_x"
      assert "a_x" in index
  
imports: import datetime
  from decimal import Decimal
  import operator
  import numpy
  import pytest
  from pandas._config import using_pyarrow_string_dtype
  import pandas.util._test_decorators
  import pandas
  from pandas import Series, Timestamp, option_context
  import pandas._testing
  from pandas.core import ops
label_desc: Use image node_id 13 for calling the TestArithmetic obj's underlying member method code with example usage: obj.test_iadd_string() without return types