code: def func(self, xp, a):
      return xp.nansum(a, axis=self.axis, keepdims=self.keepdims)
  
imports: import chainer
  import numpy
  import pytest
  import chainerx
  import chainerx.testing
  from chainerx_tests import array_utils
  from chainerx_tests import math_utils
  from chainerx_tests import op_utils
label_desc: Use image node_id 3 for calling the TestNansum obj's underlying member method code with example usage: obj.func(xp, a) and returns: xp