code: def func(self, xp, a):
      return xp.mean(a, self.axis)
  
imports: import chainer
  import numpy
  import pytest
  import chainerx
  import chainerx.testing
  from chainerx_tests import array_utils
  from chainerx_tests import dtype_utils
  from chainerx_tests import math_utils
  from chainerx_tests import op_utils
label_desc: Use image node_id 1 for calling the TestMean obj's underlying member method code with example usage: obj.func(xp, a) and returns: xp