code: def test_concat_backprop(self):
      func = compile_func(
          [
              self.input_layer1.get_activation_vars(),
              self.input_layer2.get_activation_vars(),
              self.input_layer1.get_reference_vars(),
              self.input_layer2.get_reference_vars(),
          ],
          [self.input_layer1.get_mxts(), self.input_layer2.get_mxts()],
      )
      print(
          func(
              [
                  self.inp1,
                  self.inp2,
                  np.zeros_like(self.inp1),
                  np.zeros_like(self.inp2),
              ]
          )
      )
      self.dense_layer.update_task_index(task_index=0)
      np.testing.assert_allclose(
          func(
              [
                  self.inp1,
                  self.inp2,
                  np.zeros_like(self.inp1),
                  np.zeros_like(self.inp2),
              ]
          ),
          [np.array([[[[1]]], [[[1]]]]), np.array([[[[2]]], [[[2]]]])],
      )
  
file_path: deeplift/tests/layers/test_concat.py
imports: from __future__ import division
  from __future__ import print_function
  from __future__ import absolute_import
  import unittest
  from unittest import skip
  import sys
  import os
  import numpy
  import deeplift.layers
  from deeplift.layers import DenseMxtsMode
  from deeplift.util import compile_func
label_desc: Use image node_id 3 for calling the TestConcat obj's underlying member method code with example usage: obj.test_concat_backprop() without return types