code: def test_sum(self):
      self.check_mat_rop_lop(
          self.mx.sum(axis=1), (self.mat_in_shape[0],)
      )
  
imports: import numpy
  import pytest
  import pytensor
  import pytensor.tensor
  from pytensor import function
  from pytensor.gradient import Lop, Rop, grad, grad_undefined
  from pytensor.graph.basic import Apply
  from pytensor.graph.op import Op
  from pytensor.tensor.math import argmax, dot
  from pytensor.tensor.math import max
  from pytensor.tensor.shape import unbroadcast
  from pytensor.tensor.type import matrix, vector
  from tests import unittest_tools
label_desc: Use image node_id 16 for calling the TestRopLop obj's underlying member method code with example usage: obj.test_sum() without return types