code: def string_with_modified_length(self, dtype, change_length):
      fact = 1 if dtype.char == "S" else 4
      length = dtype.itemsize // fact + change_length
      return np.dtype(f"{dtype.byteorder}{dtype.char}{length}")
  
imports: import pytest
  import textwrap
  import enum
  import random
  import ctypes
  import numpy
  from numpy.lib.stride_tricks import as_strided
  from numpy.testing import assert_array_equal
  from numpy.core._multiarray_umath import _get_castingimpl
label_desc: Use image node_id 7 for calling the TestCasting obj's underlying member method code with example usage: obj.string_with_modified_length(dtype, change_length) and returns: np