code: def test_mean_all_int64_dtype(self, xp, dtype):
      a = testing.shaped_arange((2, 3, 4), xp, dtype)
      return xp.mean(a, dtype=numpy.int64)
  
imports: import math
  import numpy
  import pytest
  import cupy
  from cupy import testing
label_desc: Use image node_id 6 for calling the TestMeanVar obj's underlying member method code with example usage: obj.test_mean_all_int64_dtype(xp, dtype) and returns: xp