code: def test_abs():
      def abs(x):
          return nd.abs(x)
  
      def grad_grad_op(x):
          return nd.zeros_like(x)
  
      for dim in range(1, 5):
          shape = rand_shape_nd(dim)
          array = random_arrays(shape)
          check_second_order_unary(array, abs, grad_grad_op)
  
imports: import math
  import random
  from functools import reduce
  from operator import mul
  import random
  from common import xfail_when_nonstandard_decimal_separator
  import mxnet
  from mxnet import nd, autograd, gluon
  from mxnet.test_utils import assert_almost_equal, random_arrays, random_uniform_arrays, rand_shape_nd, same
label_desc: Use image node_id 22 for calling a global function with example usage: test_abs() and returns: nd, nd