code: def test_backward_sigmoid(self) -> None:
      input_shape = [1, 4]
      input_data = np.array([-1, -0.75, 0.75, 1]).reshape(input_shape)
      weights_second_layer = np.ones(shape=[1])
  
      with tf.name_scope("TFE"):
          private_input = tfe.define_private_variable(input_data)
          w = tfe.define_private_variable(weights_second_layer)
  
          tfe_layer = tfe.keras.layers.Activation(
              "sigmoid", input_shape=[4]
          )
  
          dense_out_pond = tfe_layer(private_input)
  
          loss = dense_out_pond * w
  
          # backward
          _, d_x = tfe_layer.backward(w)
  
          tfe_loss = loss.reveal().to_native()
          tfe_d_x = d_x.reveal().to_native()
  
      with tf.name_scope("TF"):
          tf_layer = tf.keras.layers.Activation(
              "sigmoid", input_shape=[4]
          )
  
          x = tf.Variable(input_data, dtype=tf.float32)
          w = tf.Variable(weights_second_layer, dtype=tf.float32)
  
          with tf.GradientTape() as tape:
              y = tf_layer(x)
              loss = y * w
  
              # backward
              d_x = tape.gradient(loss, x)
  
          np.testing.assert_array_almost_equal(
              tfe_loss, loss, decimal=1
          )
          np.testing.assert_array_almost_equal(tfe_d_x, d_x, decimal=2)
  
file_path: tf-encrypted/tf_encrypted/keras/layers/activation_test.py
imports: import unittest
  import numpy
  import pytest
  import tensorflow
  import tf_encrypted
  from tf_encrypted.keras.testing_utils import agreement_test
  from tf_encrypted.keras.testing_utils import layer_test
label_desc: Use image node_id 3 for calling the TestActivation obj's underlying member method code with example usage: obj.test_backward_sigmoid() without return types