code: def test_std_all(self, xp, dtype):
      a = testing.shaped_arange((2, 3), xp, dtype)
      return a.std()
  
imports: import math
  import numpy
  import pytest
  import cupy
  from cupy import testing
label_desc: Use image node_id 16 for calling the TestMeanVar obj's underlying member method code with example usage: obj.test_std_all(xp, dtype) and returns: a